I`ve got the following system:
Intel p4 2.4 Ghz, 1024mb RAM (DDR 333 mhz) - two blocks but not from the same manufacturer s o I believe dual channel is not possible.
VIDEO CARD : Geforce 3 Ti 200 64 mb video RAM
MOTHER BOARD : MSI

PROBLEM : Whenever I try to play some game that uses a bit more complex 3d graphics my computer freezes after app. 15-20 min.
I`ve tried all the possible things to do (downloading latest video drivers,defragmenting my drive even change some settings in BIOS or direct x 9.0c, but nothing seemes to help.
Here are the games that causes problems :

Max Payne, Call of duty, PRO evolution soccer 4 and some more.

Please help!!

What you describes sounds like an overheating issue to me. Could be either the CPU or GPU.

Try running one of the games witht he side panel off and a house fan or some other air source blowing intot he case. If you can run it that was without a lockup, then the issue would almost definitely be heat. You can try to rectify the problem by adding a fan or two to your case.