I'd be interested in any responses to this question as well. I've got an AMD64 CPU, 2GB of RAM, Win XP SP2, and now I can't seem to have an application running for 5 minutes without the system hanging. At first it seemed local to just a couple of apps (iTunes, Picasa, AVG Free Edition), but it seems worse than that now.
I don't know if the details of the hang help, but I can still see my cursor, and can still even come back from screen saver, but I can't click on anything, and CTRL-ALT-DEL doesn't do anything, either. I have to reboot manually, and it doesn't create any minidump file or anything.
I've run CHKDSK, I've run Spybot and AVG Anti-Spyware, I've tried defragging, but that tends to get stuck, too.
Lately, it's also been losing my Quick Launch toolbar when I come back up. Don't know what that's all about.
I've updated video drivers, replaced a CD drive that seemed to be mostly dead, uninstalled and reinstalled programs that seemed to have problems, removed Google Desktop in case that was a factor. None of it has worked, although the video driver update seemed to fix a problem I was having with audio playback.
I've been reluctant to reinstall XP because if that doesn't work, then I have to admit total defeat. Any guidance here would be very, very helpful, as I'm way past my expertise here.