Same problem here, I've figured just about everything else out on my own. I'm running a V1.6 Box with the Executer 3 chip, 80gb, blah blah... I have the newest version of XBMC and the newest version of Orbs (Which still won't show the weather info on the dash!)
I scan my movies with IMDB and it only found 8 out of 37 movies. These are all DIVX and I made some of them and DL'd others.
I tried the .tbn trick and no luck, I have all 37 of my movies in one folder with very simple titles like:
Days of Thunder.avi
Anchorman.avi
etc...
Is there a setting somewhere to get XBMC to see the thumb?