BSOD on boot

I get this

A problem has been detected and windows has been shut down to prevent damage to your computer…

then at the bottom:

Technical information:

***STOP: 0x0000007B (0xF9943640, 0xC0000034, 0x00000000, 0x00000000)

when i boot my windows machine (Dual 933Mhz Intel Pentium III, 512MB Win XP home)
what could be wrong

See if this helps:
http://support.microsoft.com/default.aspx?scid=kb;en-us;324103

Mac, minidump issues:
http://www.jsiinc.com/SUBJ/tip4900/rh4981.htm
http://www.microsoft.com/whdc/devtools/debugging/default.mspx

The best advice for you, in my opinion, is to copy the error number on the blue death screen. Then google parts of it to see if any related problem is on the Internet. Besides Google also you can use MS knowledgebase like Bob posted (http://support.microsoft.com/search/?adv=1)
a free memory tester (run it overnight) (http://www.memtest86.com/) or XP error explanations (http://www.xptuneup.com/xptuneup_stopmessages.htm).