In my opinion:
use all of these tester to test your important computer memory:
Memtest86
http://www.memtest86.com/
there is good article for memtest86:
http://news.zdnet.co.uk/hardware/0,1000000091,2132568,00.htm
Memtest86+
http://www.memtest.org/
The detail for windows memory diagnostic:
http://oca.microsoft.com/en/windiag.asp
