Win XP x64 crashing

[Seeq]

Just put together my 64bit computer, Athlon XP 64 3000+ (winchester), Crucial 1GB (512x2), MSI K8T Neo2, 40GB and 200GB IDE, Sony DVD-+RW, TDK CD-RW, ATI 9600XT. Everything boots up fine, installation happend without a hitch but now it randomly just crashes, screen goes black. It will run just fine if I do nothing or tool around the OS (the HDs and stuff), but as soon as I start up a program it could crash at any moment. Usually within seconds of opening firefox or IE it quits. It seems to happen only when on the internet. Not sure what I can do. I cleared the CMOS, installed latest Catalyst drivers and mobo drivers. Any suggestions?