See my new four-monitor/quad-head/six LCD set up at uni and at home!
Grab yourself a dual-headed video card and have a real hard time aiming at your opponents!
How to set up dual or multi-monitor gaming?
To enable Quake III to render at an arbitrary resolution, edit your q3config.cfg file and change/insert the following values:
seta r_customheight "1024"
seta r_customwidth "2560"
seta r_fullscreen "0"
seta r_mode "-1"
Replace width & height with the values you choose. Since it'll start in Windowed mode, you'll need to ALT+TAB to another application
to regain control of the mouse (or ALT+CTRL+DELETE to open the task manager, or ask Quake III to release the mouse nicely - can't remember the command now). Once you have the cursor back, right-click the title-bar (to prevent it regaining the focus),
select 'Move' from the system menu and re-position the window so it fills your monitors!
I have used this method to stretch Quake III over 3+'a bit' monitors (unfortunately not 4 due to hardware limitations).
I've also done this for Unreal Tourament 2003. It involves the same process of changing to windowed mode and editing the config file to set your custom resolution.