I purchased an "open-box" N810 recently. Whomever bought and opened it prior to me has all their information in it. For example, his skype account, his email, etc. How do I delete all of his info and accounts and set all that up as myself?

reflashing would be your best bet. There are windows options, and linux options, depending on your persuasion.

Okay, how do I "reflash"? I've got a macbook but I can run windows xp on it through parallels. Do I need to connect it to my computer to reflash it or is that something that I can do on the device itself?

http://wiki.maemo.org/Updating_the_tablet_firmware
That link tells you how to reflash. If you've got a lot of good applications you use on your device you'll want to use the backup program to make it easy to reinstall those applications after reflashing.

I'm trying to reflash it according the those instructions. I'm following the directions for Mac OSX:

1. Download the 770Flasher (yes, it will work fine for flashing an N800 or N810).
2. Follow the steps above to get the appropriate firmware image.
3. Drag the firmware image (will end in .bin) onto 770Flasher.
4. Follow the on-screen prompts.
5. You should now see Suitable USB device not found, waiting, switch on your tablet while holding the Home-button.
6. Watch the messages as the image loads to the tablet after which it reboots automatically.

The firmware image I download is titled:
"RX-44_DIABLO_5-1.2008.43-7_PR_COMBINED_MR0_ARM.bin", attachment

When I open the flasher, it asks what image I would like the flash and I select the above firmware image that I downloaded. The Flasher says the following:
flasher v0.8.1 (Jun 8 2006)

flasher v0.8.1 (Jun 8 2006)

FIASCO subimage data length mismatch
SW version in image: RX-44_DIABLO_5.2008.43-7_PR_MR0
Image 'kernel', size 1536640 bytes
Version 2.6.21-200842maemo1
Image 'initfs', size 2327808 bytes
Version 0.95.22-200842maemo1w38b3
Image 'rootfs', size 125435904 bytes
Version RX-34+RX-44+RX-48_DIABLO_5.2008.43-7_PR_MR0

When I drag the image (the .bin file) onto the flasher nothing happens.
What am I doing wrong? I'm pretty unfamiliar with this type of technology. Some step by step instructions or troubleshooting would be great.

I'm a bit confused about the new fiasco flasher thingy.... if I've got the latest OS.bin image saved to mmc can I now totally reset the device (flash as new) from the commandline?