http://www.emsai.net/projects/widescreen/fovcalc/This calculator should help you modify game or program configs that need "tweaking" to support Widescreen properly.
The only problem I've personally found is those servers relying on anticheat stuff will revert your FOV back to the default value (usually 90), or might even kick you out in the worst case.
For offline playing and on certain non-competitive servers, it works fine.