I have an N800 from Ebay being shipped now. Will probably get an N810 too, as they are cheap toys. Being semi-retired, I have time to play with them. With the Nokia Software Update Wizard, it only takes a couple minutes to try an OS and there seems to be a lot of programs for the N800's.

I'm hoping the N800 will deal with my wifi better tnan the 770.

You shouldn't have any probs with the n800 and wifi.
I do suggest the walkthroughs and the links in my signature to get the most out of your n800 or n810.

I'm definitely going through your stuff.
Also just bought an N810 on Ebay.

Will I need to format the SD card for the N800?
Will I need to do anything to use 64GB card?

It depends...
fat32 is the natural choice for simply having stuff...movies, music, books, etc...as storage for your NIT.
I suggest freshly formatting a card on your pc with a format utility..I believe I mention one of the best with a link to it ...it will work on win7 as well...esp. a new card before doing anything with it.
If intending to run an os off a card...precautionary 1st step is to format to fat32 (just in case) then follow the walkthrough for the easiest method of getting everything set up.
It's all explained thoroughly and simply...
the vid walkthrough should help as well...
if you have any issues that can't or aren't explained thoroughly...
tell me and I'll give you a hand in whatever way I can.

64 gb cards and higher can be sketchy ...
Best suggestion is 32gb and lower...
class 4 sdhc cards
you can use higher classes..
but the sweet spot is class 4 ...
the speed of higher can be problematic depending on your usage of it on your NIT

Although I left topic long ago, have you tried something like this?

http://mobinubi.com/update-nokia-n800-to-5-0-lollipop/

That I would not attempt.
They are misleading.
It isn't a nokia n800 they are talking about here.
More like mistakenly referring to the nokia n8-00 or nokia n8 in word only.
The methods of putting android or rather nitdroid (in particular for the actual n800) are not as simple nor as easy as is suggested.
The performance and functions which do not work consequently do not make it something I would flash over diablo turbo for.
There are chances that it will fail and potentially brick your device.
As well it is not lollipop...much older version of android / nitdroid which is compatible as well ...for the nokia n800.
I would avoid trying this at all costs.
The photos aren't even of a n800...not a NIT anyway.
Ordinarily I wouldn't suggest android / nitdroid on the n800...
except for research purposes by an individual knowing exactly what they are doing.
There are faaaar more os's easier, more interesting and that have more functionality to try with the n8x0's.
In point of fact ...my best suggestion in this regard is Easy Debian...
Even though it is old ...it still works admirably.
There is a huge long list of os's which individuals have gotten to run on the n8x0....to one degree or another of functionality.
I'll post a list of them all...the ones I know of and have researched...which is I believe all of them...here on this thread tonight.
It is a pretty long list I think you will be happy with.
But yeah ...normally I'd suggest avoiding installing android / nitdroid at the best of times for new people...
But this page isn't even meant for the n800 NIT proper.
Do not attempt.

Thanks. Will not go there. Would appreciate list of other OS to play with. N800 & N810 should arrive soon.

this list is of os's is not just a list of os's which fully function, but also os's which partially work to lesser or greater degree, and some os's work well still or used to work..but are incurrent disrepair and need work, are simply mentioned, referred to, or individual work has been done concerning them with the n8x0 ...
keep all that in mind.
there is a folder (somewhere around here) with I believe...browser bookmarks for easy reference instead of hunting for hours on end...

-Acorn
-Archimedies
-Risc os
-Angstrom
-Arch
-Atari800
-Deblet
-Dos
-Easy Deb
-Easy Mer
-Garnet (Palm os)
-Gentoo
-KDE
-Basilisk (Mac)
-Meego
-Mer
-MSX
-Openwrt
-Windowmaker
-Ubuntu (easy)
-E17
-Opensuse
-Mamona
-Poky - Yocto
-Funtoo
-Nitdroid
-XFCE
-Fedora
-Inferno (Plan 9)
-Emdebian
-Slackware
-AROS (amiga-esque)
-Linpus Lite
-Open Solaris
-Backtrack - Backhand -Kali
-Zenvoid
-BSD
-Win 3.1
-goowy, open webos, webos and such...
- other arm ports as well such as reactos have either done some work or mentions...
I may be forgetting some...
anyone who knows of any os missed ...chime in.

Then of course there are a handful of window managers as well...not to go into that..there aren't a ton...a few...but for now...this is about os's for the n8x0...

Just received my N810, not a scratch on it.
It has OS800HE already installed.
It connects to the internet, unlike the 770.
I get numerous "Secure connection" messages. Any cure for that?
Also, with Skype, I get message to turn cookies on. ??

Good.
It's in decent shape.
Nice that it has stock os2008 on it.
won't be HE though.
Stock is stock.
And that could be either chinook or diablo...
odds are it is diablo.
The odds it is diablo turbo are thin to zero.

To enlighten you some on the state of most purchased n8x0's and for the most part n900's I have purchased....
and I have purchased many...
given quite a few away to friends, family and colleagues...
99% of all n8x0's and n900's I have bought were either at stock or earlier firmware...and in ok to dubious shape all the way down to seeming pretty much bricked to a paperweight, quasi-bricked or appeared to be fubarred ..due to the past owner not knowing how to handle and take care of their device [and believe me it takes a lot of negligence and poor care over many years to foul the onboard firmware...]...and all were at latest released "stock" firmware or earlier...the same issue..the past owner not understanding or curious enough to explore the device...[ie- a number of n8x0's I have received were at chinook or earlier iterations. and a few n900's were at stock fremantle..or at best pr1 ...]. Most people who have purchased / purchase a n8x0 don't know the 1st thing about them or know what to do with them or have the curiosity or perseverance to do anything with them past installing applications from the download page here at maemo.org
They just don't know or don't care enough or are not curious enough to look for solutions to common issues.
And with time their device starts acting buggy ..has issues..and they just sell it...instead of dealing with it. Whether all it needs is a simple fix[es] or reflashing. or backing up their os onto a computer so...if there are issues...simple cloning of their perfect setup is quicker..and they haven't lost a heartbeat of time with setting everything back to the way they enjoyed their device from the dead start of reflashing.

You are fortunate that you got one in decent shape though.
Aren't they little tanks?
Solid solid solid.
Anyway.
Concerning your "secure connection" and "skype cookies" issue.
Let's solve that in one simple easy clean sweep.
Whatever is going on with that device currently is not relevant.
There are only 2 points to follow when getting a new / used unfamiliar (in the sense that it is unfamiliar to you as to what has been or hasn't been done to the device.) n8x0 (or n900 for that matter).

Point 1 - Don't bother fiddling with, adding to, subtracting from, trying to puzzle out whatever previous user generated problem there may be on what exists on it when you receive it.
In fact I suggest NOT powering it up anymore than absolutely necessary until you are ready for point 2.

Point 2 - Get a decent battery ( if it came with a decent battery that will hold a charge properly and for a good length of time...in a pinch a beater battery 2-4 hour charge may do....best is 6-7 hour charge..I don't highly suggest it...but I have done alllll that is necessary with a battery that was just old and beaten...I managed with a battery which could only hold a chage for 60 minutes...I don't suggest it ....unless you are a masochist....since you spend alot of time letting the bugger catch up in it's charge before continuing with the process of setting up your n8x0 properly...) plug in your n8x0 to a wall outlet (don't power up) charge your battery fully. Get your usb to micro usb (for n810) ( for n800 it is usb to mini usb cable) (AND MAKE SURE YOU HAVE BASIC CONNECTIVITY BETWIXT YOUR N8X0 AND PC....you may need libusb installed..but that is all explained in said walkthroughs...) and go straight to "Pimp My n8x0" in my signature.
Read.
Read it twice.
Read it thrice.
Do exactly what instructions there are.
(And people...everybody... really...
it may seem very difficult and scary...
but it is actually very very very very easy...
for goodness sake follow through with the walkthrough and clone your os to an sd card.
There is the option not to....but only for the exceedingly timid.
The process isn't much more time consuming or difficult...
In fact cloning will save you time later if / when you have any problems...
and the benefits and empowerment you will get from it make the whole of the endeavour very worthwhile.
Hell....fundamentally it saves wear and tear to the onboard system....
if anything goes horribly...terribly wrong afterward..
with your system...
after cloning ...
it isn't the device that takes the hit and at worst gets bricked...
it's the cheap and disposable sd card that takes the beating...
and you simply reinstall onto a new sd card or clone your backup from your pc.....
Actually-actually....you could...after you get the swing of the process that is...clone the same pristine clean os onto a second partition on the same sd card...sooo...you have in fact ...a duplicate of your os ...twice...one to screw up ...and one ready to play with once you've screwed the 1st one up ...saves a whole lot of time...and makes things safer to experiment with...the best and safest set up there is for any device-line.)

So forget messing with a previous owner's issues.
Get ready to do what's gotta get done.

Hmmm...
I wonder...
Hallllllo Mr. friendly neighbourhood Moderators?
Could we move the entirety of this thread to ....say the os2008 subforum?
I know it is titled nokia 770....
but the majority of the content has moved to diablo-esque content.
and there is a great deal of info here which I'd hate to see get swallowed up in the "General" subforum and get lost....