I've had a lot of success using Iriverter, a free open source program. It was originally created for iRiver devices. But someone created a profile for the Creative Zen W (which I also own). The profiles are just text files that are easy to edit.

So I have created a profile for the N800, and it seems to work fine.

Use this for converting avi files (Bittorrent is your friend!) or ripped DVD's (use DVD Shrink to rip the movie to a single vob file).

I've uploaded it here:

http://www.mediafire.com/?umg9tmnj0hm