Check out this article on shacknews to enable widescreen in Quake3 engine games.
"I finally got around to sharing this little trick with a friend the other night and thought a lot of you guys might enjoy it. All Quake3 engine based games have the ability to play in widescreen letterbox mode. Im not talking about adjusting your FOV, but actual non-distorted widescreen mode [screenshots here!]. 856x480. The only trick is getting your videocard to recognize the resolution correctly. That takes a bit of .INF or registry magic."
News source: Shacknews