These two programs offer tests to run from inside windows to torture test (free) memory. I have used both of these to help identify a dead stick of ram (out of two that were in a laptop).
This one - a little annoying since it displays a dialog box on each error, though, I guess it doesn't really matter, there should be zero errors when testing ram...
http://hcidesign.com/memtest/
I like this one a bit more:
http://cpu.rightmark.org/products/ramtester.shtml
Some other cool tools on that site too.
MemTest86+ Notes
Tags: ram, memory, bad, stick, test, buggy, bsod, windows, writes, reads