Windows XP has encountered a problem?

I have a dell xps 400 with 2 gb RAM 2 pentium D processors at 2.8GHZ and a nvidia 8800 gts gpu running on windows xp sp2, when I play games theyll play for a little while but then ill get a msg that says windows has encountered a problem or something like that srry im not sure xactly but its like that n it gives u the option 2 send a error report n then it justs exits 2 desktop, can ne1 help me fix this please? and no reinstalling windows or reinstalling the games deosnt work ive tried both of those already.