sorry if this should be moved into the hardware section but i am trying to run games if i get this working.

ok my comp's specs:
ASUS P5GD1
Intel P4 530J S775 3.0GHz (auto OC with mobo up to 3.6ghz)
Sapphire ATI Radeon x850XT
2GB pc3200 dual channel
Fedora Core 5 2.6.17-1.2139_FC5smp
Xorg proprietary display driver

ok so my problem:
I am relatively new to linux but my dad is a genius with it. although since he never uses a computer specifically for games, im on my own on how to figure this out. Right now im running FC5 2.6.17. ok so first i decided to download the Doom3 demo to test out how well it would run. but when i start it i get an error. so then i downloaded America's Army, only to find that it too had a problem and can't execute. also it said some about the virtual memory being too slow. finally i downloaded UT2004 demo, which actually runs, but very very slowly. for an x850xt i should be running that game easily with all settings maxed. so now i have a couple questions i hope someone can solve for me.

1. I know about virtual memory from windows and how you can set the size. is there some way i can increase the size in linux?
2. is there another company or something that makes optimized drivers like Omega does for windows? if not, how can i configure the driver to be 3d accelerated?
3. is there an overclocking tool i can download to set my clocks higher?

any help would be great. thanks.

Generally these sorts of problems occur when the correct drivers aren't present.

Generic drivers are nrmally there that give you basic functionality like good colour depths and res' but for things like 3D accelleration and OpenGL support, you need the drivers.
And ATI has alot of catching up to do on Linux drivers