game problems lag

[KingTKS]

OK i built a new system. i used to have an amd system but i decided to go intel this computer and here is what i built.

asus P5GD1 915P
Pentium 4 LGA 3.0 800FSB 1MB L2
Corsair pc3200 256x2 platinum
enermax 485 dual 12v rail
Sony CD-RW/DVD combo
Western Digital 200GB SATA
ATI X700 Pro 256MB
Windows 2000 Pro SP4

I updated the latest Chipset drivers, graphics driver, and direct X

my problem is when i go to play a game Doom3 or halflife 2
the game really lags. like i think i'm getting around 15FPS but i'm not sure
it just lags really bad. i turn down the settings all the way and it still lags. i can't figure out what the problem is. I ran DXDIAG and all the tests came out good. any suggestions on other programs i should try to test out my stuff to see whats wrong with my system?

 

[KingTKS]

And yes i tried winows XP and it still didn't help