I've always loved windows 2000, I could run it for over a month without a reboot easily while using it every day heavily. Then, all of a sudden, 3 days uptime was a lot to ask for. Usually around the 3rd day, programs would stop launching and windows would be drawn wrong. Menus would stop popping up. Basically anything which required memory wouldn't work unless I closed some other stuff to make room for it.
I dealt with it for months (I guess I was just too lazy to troubleshoot it) but finally I nailed it down. mIRC 6.x was to blame. It was the first thing I launched when I booted up and the last thing I closed before I shut down. Now I'm running 5.91 and I think things are back to normal. I will post back here if I find that I still have the problem, but so far it seems that mIRC 6.x was to blame. I really liked 6.x for its multi server capabilities, but it's really unusable. One thing to note is that I was using 6.x with the Polaris script which was originally written for 5.4 or something, though I doubt that is to blame for the problems. I don't think I'm the only one with this type of problem either. It's been a long time, hopefully a new version of mIRC will be released with some major fixes.