With very intermittant faults I use Microsoft memory diagnostic extended tests and run it over night for 8 or 9 hours. If it finds errors it lists the data and the address and carries on.
If you are not familiar with this it is downloadable as an iso image which you burn to CD and boot from, the test starts immediately.
It once found a fault that was causing a BSOD about once a month at an address between 3.0 and 3.2GB, I haven't had a BSOD for 18 months now.
I have been using Windows 7 since the Beta version and have been marvelling at how well it has run, in fact, the few problems I have had have always had simple fixes. This was with the 32bit OS on my Compaq Presario V6200 laptop. I recently built a new desktop machine and because I have 4GB of ram (Corsair DDR3 1333 high performance) I installed the 64bit OS (Windows 7 Ultimate full retail). I have an MSI 770-C45 mobo and because it has no integrated video, I have a nVidia GeForce 7900 GS video card. All components test fine. But ever since first booting this machine I get random lockups when using Internet Explorer 8. It doesn't seem to be when I'm at any particular website (though it has happened several times on this site). Everything is fine and then suddenly everything just stops working, mouse, keyboard (which are USB wireless devices) and programs. However, the Sidebar clock's second hand continues running. It does no good to unplug and reinsert the mouse/keyboard USB transmitter, as it is not being recognized, which forces me to hit the reset button. When Windows restarts the screen that says in was unexpectedly shut down comes up, but it is on the "Start Windows normally?" line and has no indication of what might have happened. This problem happens only occasionally, but as such things go, it's usually when I'm in the middle of doing something, like typing this post, so it is extremely annoying when it does happen. I should also say that I am using the 32bit IE8 as I have read that there are website compatability problems with running the 64bit IE8 (though I have not tried using it myself). I bring this up here because the Microsoft forums are less than useless for getting relevant information, no one ever seems to understand what my problem is and always give me suggestions that have absolutely nothing to do with my issue. So, I hope someone here can help.