100% CPU usage when play game after minutes

Datasunny,
When you say 512MB RAM I am assuming that is your system RAM, correct? What games are you trying to play exactly? Once it freezes can you hit "Control + Alt + Delete", if you can try to take a screen capture of the Performance Tab and attach that to your new post or feel free to send me a private message.

With these specs I would make sure your in game resolution is not that high. Also, you might want to turn off all the extra eye candy features.

Thanks for your reply.
My screen resolution is 1024X768, my laptop only supports 1024X768 or 800X600.
The games i found with problem are pretty much any 3D games. Say Counter-strike 1.6, Prince of Persia: The Sands of Time, Tom Clancy's Splinter Cell (the first version); all pretty old games which didn't ask too much resources.
Maybe i didn't describe clearly in my previous post, in the first 5 ~ 10 minutes playing, everything's just fine, but suddenly the cpu usage of *the game i played* jumped to almost 100% and the fan started blowing. The game didn't freeze but moved *frame by frame*.
I did turn off any features which can be turned off in games, like special effects. But didn't help too much.