crashing board

[/dev/null]

my rig keps crashing whenever i put it under stress
i.e I can write code,do email etc all day long with no prob but when i deathmatch in Q3 and the rockets start flying and the chainguns start spinning,my PC crashes
this is not cool
my specs are
ASUS A7n266 mboard with onboard geforce 2 and sound
AMD XP1700 + CPU (runs at 1426 MHz)
512 Mb 266 DDR
20 Gb HDD (new,no bad sectors)
im running winXP and ive tried the service packs and reinstalling XP
ive even tried installing win2000 and 98 but to no avail
id like to find the problem without selling my board so i can get a second rig but otherwise im gonna do an upgrade and sell off the current board
plz help

[SteveI]

Welcome to AOA /dev/null,

What memory are you using? also, what PSU, and what are you using for cooling? what are your temps?

[/dev/null]

im at work right now so i dont have the exact specs on hand but the CPU (PSU?) is an athlon AMD Xp 1700+ and im using 512 MBs DDR 266 (2 * 256 meg chips) as i said i dont have the temperatures on hand but ill definitely check it out when i get home

[SteveI]

Do you know if your CPU is a Palamino, TbredA or TbredB?
More importantly, a PSU is the Power Supply Unit.