I like to play my games in windowed mode. These days, pretty much anything I play is in a window, and for the most part, it works fine. I have run into a couple exceptions, and given the nature of these exceptions, I'm quite perplexed.
The first is in Civ4: Beyond the Sword. I used to play regluar Civ4 in windowed mode with absolutely no problems whatsoever. But when I enabled windowed mode in BTS, my framerates dropped to less than 1FPS, despite the processor usage only being around 40-50%.
The second instance occurs in World of Warcraft. I know I'm not supposed to talk about that here

but this instance is very odd. I have both an European and a North American version installed, though I only actually play the North American one. The European one is a holdover from my Irish adventure. But one day, I decided to log into the European version and say hello to all my old guildmates I hadn't seen in ages. I enabled windowed mode, and Pow! Less than 1FPS there too. And yet my NA version runs in windowed mode with narry a hiccup.
So I'm befuddled. Anyone have any ideas as to what might be causing the slowdown?
Specs:
AMD Athlon 64 X2 4400
ATI 1900XTX with 512MB RAM
2GB System RAM
A crapton of HD space, with about 25GB free