Intel 82845G Graphics controller
EW i remember that thing, it sucks at high resolutions!
Things to try in the console:
r_flares 0 (OA also has flares that work, Q3A does not)
r_fastSky 0 (Some sky textures have a ludicrous amount of layers)
r_detailTextures 0 (Unlike Q3A, OA actually utilizes this setting for layers of detail patterns similar to Unreal)
r_bloom 0 (If you don't have a Geforce3/Radeon or better, you shouldn't use this.)
You could also play with r_primitives (0, 1 or 2 - higher settings will 'freeze')
No, vertex light hardly makes a fps difference.
Another thing could be software mode kicking in for some reason when it shouldn't.