you could turn off compiz, or you could use this script, which turns off Compiz during the time you're playing Open Arena --This script works on my laptop running Open Arena 0.7.6, it should work 0.8.0, or any other opengl app (Just change the path to the application)
I'm also using Ubuntu 8.04 btw, but same as before, this should work on every version of Linux
#!/bin/bash
metacity --replace &
/home/(username)/openarena-0.7.6/openarena.i386
compiz --replace
The only issue I have with it is that at times, the default mouse cursor appears on the screen, just to the side of the target marker, rectile... that dot that I can't remember the name of...
but I still have mouse control over the game
The fullscreen-window with freaky colors happens with all versions of OA on Ubuntu 7.10 and 8.04, I get that all the time. Best way is to turn off the screensaver during gameplay (I have no scripts for that though...)
tell me if that script works, or if it just causes a lock up, That's all that I know