I set the game to run in windowed mode, will this interfere with anything?
Hmm. I'm not sure, I never bothered to test the mod running in windowed mode. It's entirely possible it may not work.
Before looking into this any further, you should first verify that the game runs with the mod applied in non-windowed mode ok. If not, there's likely an issue with how the mod was applied. If it does run ok, then we can assume it's a problem specific to windowed mode (and unfortunately there's probably nothing we can do about that).
1920x1200 doesn't work...
All resolutions supported by the mod have been tested and verified. The screenshots in the DR at the start of this thread demonstrate 1920x1200 running successfully and correctly.
With no info to go on, all I can say is follow the instructions here as carefully as possible: http://www.widescreengamingforum.com/wiki/index.php/WSGF_Hacks_for_SW:KOTOR
If you're having trouble with a specific step, be detailed when explaining what you did so far.