X crashes, that isn't a reboot. Try this
cd /pathto/your/oa/
./ioquake3.i386 +set r_allowSoftwareGL 1
Either the Savage driver isn't fully hardware 3d OR the game is trying to change to a resolution your video card doesn't support. If the above command crashes X you'll have to start the game using
./ioquake3.i36 +set r_customwidth X +set r_customheight Y
where x + y are your screen resolution, alternately add the resolution 640x480 to xorg.conf if it is not there in the screen section, like so:
Section "Screen"
Identifier "Default Screen"
Device "Generic Video Card"
Monitor "Generic Monitor"
DefaultDepth 24
SubSection "Display"
Depth 1
Modes "1024x768" "800x600" "640x480"
(assuming you aren't using xorg 7.3 yet which has done away with the configuration file except for proprietary drivers).