Could this program work for the N800?: Acala DVD 3gp Ripper
http://www.cutedvd.com/html/dvd_3gp_ripper.html

I have converted 2 of my DVD movies with Acala DVD 3gp Ripper(for phone), but I do not have a large enough SDcard to insert into N800 to test.
Files range from 153MBto 320MB in size and have the extension 3GP, Mpeg-4 codec, and frame size 176x144(320x240 can be chosen).