So because my brother sent me a free trial of World of Warcraft, I gave it a try. It worked surprisingly well on my 800MHZ, 384MB RAM, 24-bit color Windows 2000 PC. It had a little trouble when I went into some of the capital cities when there were tons of players around, but otherwise worked perfectly.
I really don't want to be wasting time on WoW, so I'm not going to get a subscription. Over the last week I poked around a little at some of the other free MMORPGs, and none of them even slightly worked on my PC. Either they didn't like Windows 2000 or barfed on 24-bit color. Most of them wouldn't even tell me why they bombed out.
That's pretty pathetic programming for all these other games since WoW seems to have much higher quality game graphics and should have had much higher system requirements.