Have a look at the dump on screen to see what might be causing the crash. Check for repeated words, like KERNEL32, or NTLDR.
Can you give us the actual message? i.e. "WINWORD.EXE casued an invalid page fault in module xxxxx".
If it's consistently the same file, try reinstalling that app.
Alternatively, it could be hardware related. Try removing one of your RAM chips (if possible) testing it, and then swapping over and testing the other(s). Try running a thorough scandisk or chkdsk, torule out HDD problems. Make sure you have plenty of free space on your drive.
If you can give us more info, we can give a more specific answer.
Hope this helps,
Gary