Quake 3 Arena is a game that has introduced a new engine used in several games, including Star Trek - Voyager Eliteforce, Wolfenstein Enemy Territory and Call of Duty. The game in its unmodified original version, however, has a rather limited set of possible resolutions, which usually don't cover all possible resolutions of the graphics card, especially not many wide screen resolutions. However, you can still set these resolutions by editing the right config files for the affected games:
seta r_mode "-1" seta r_customwidth "x" seta r_customheight "y" seta cg_fov "z"
y for the x- or y-resolution.
z is selected depending on the aspect ratio. For 4:3 the value remains at default
80 (you don't need the line at all), for 16:9 it is
95, for 16:10 it is
90. Of course, the specified graphics mode has to be supported by the hardware, otherwise it'll end up blowing in your face.
The name of the respective config file may change, but at its core it is still the same engine with the same engine dependent parameter names.