I've discovered most of the guides for tethering (using the N900 as a modem for a 3G data connection on a laptop) seem to assume you use Ubuntu and have a full gnome environment.

Took me a while but here is another simple way:

Install wvdial.

Edit /etc/wvdial.conf to look like this:
Change VirginInternet to the ID of your provider. Generally most have blank username and password. Otherwise use the username and password in "quotes" where it says blank. (took a while to work that out)

To use it:
1) Disconnect the data connection on the N900.
2) Plug in the USB cable, and select PC-suite mode on the N900
3) run wvdial via a terminal window, or a shortcut on the desktop, leaving the window open in the background.
4) ctrl +c in the wvdial terminal window to hang up.


The above is based on the debian wiki, and my modifications to make it work on my phone. http://wiki.debian.org/UseYourCellPhoneAsModem
Seems that if you run "wvdial blz-scb" should dial out over a bluetooth link if you set that up too.

Hope this helps other googlers later

ubuntu uses networkmanager, that has kde client as well. as well there is wicd, last time talked to devs(long time ago) they promised a lot of tasty things in 2.0, you prob should check it and if it doesn't work to talk to devs to add on freenode #wicd or to make request on their bugtracker

I use Wicd already, and it's pretty good apart from occasional suspend/resume issues. Haven't worked out how to use it for this though. I've never managed to get network-manager working for any wireless connection on either of my computers. Even retired it for this, and still failed. aptitude purge network-manager once again.

Happy the above works, and it seems pretty robust compared to my forays into point and click setting up.

Network manager was troublesome on wifi connections (sudden loss of network visibility) so I also used wicd but then they messed it up (it couldn't connect because password was always wrong) so with 10.04 I switched back to NM and this time it works perfectly, no issues at all. And connecting via USB on 3G network works perfectly and it was very easy to set up. Ubuntu has detected 3G modem and all I had to do was to select my provider from the list. And that's it.
And wicd still doesn't support broadband.

I'm using USB-tethering with NM on Ubuntu NBE. On Mint and Peppermint NM was really acting up with WLAN (needed usually a reboot after 1-2 hr connection), so I tried WICD. Very stable, good UI, BUT a no-go with WLAN tethering with N900. Now, NM is starting to act up again on WiFi, while ad-hoc seemed to hold well. So, I'd love to switch to WICD again for the WLAN stability, but I fear I the hoops are many I must go through to get N900 tethering to work

@ frostbyte
tray adding NM repo to sources. I noticed that it acts much better with those small frequent updates then only with official ones from ubuntu.

thanks, didn't even think of that, still learning linux...

I've also successfully used wvdial on my n900 and Debian Lenny laptop via both usb cable and bluetooth.

go to joikusoft.com There is an affordable program that makes a hot spot out of your 3G connection. It works with any laptop or computer that has wifi. Really cool. I use it all the time, and my friends with their usb internet sticks are jealous as hell that I have a portable hotspot for 10 bucks a month.

I'd recommend you to change the title to something like "N900 USB tethering with Ubuntu" for better future reference as there're WiFi tethering, Bluetooth-DUN tethering and Bluetooth-PAN tethering.