Widescreen Resolution for Doom3

I have been looking thru all the major guides on the web on how to enable widescreen resolutions and nothing seems to work. I've tried altering the DoomConfig.cfg and added the AutoExec.cfg file and everything that they says works but they don't. I can't even switch it from 640x480 to 1280x1024 using the ingame options it just keeps being set to 640x480. Any help?

seta r_customHeight "your size"
seta r_customWidth "your size"

in the doomconfig.

Also here is some info that you can try to get it to work.

r_mode [-1,3,4,5,6,7,8] - This setting determines the resolution, as set in the in-game menus under Screen Size (See In-Game Settings section). The mode values are 3 = 640x480, 4 = 800x600, 5 = 1024x768, 6 = 1152x864, 7 = 1280x1024 and 8 = 1600x1200. Note, you can use -1 for r_mode, and this tells the game to use the values for r_customHeight and r_customWidth to set screen width and height - this is useful for allowing things like widescreen mode.

Have done that and it still didn't work.

Have you tried setting r_mode to 7.

go here, youll be surprised what they can offer.
Doom 3 - WSGFWiki

read this? TweakGuides.com - Doom 3 Tweak Guide