Post your hardware too!

I'm having problem with World of Warcraft ~Wrath of the Lich King~ under Windows 7 build 7048 x64. When I play in window mode, I maximize and play at really good frame rates, better than in Windows Vista SP1 x64. But, when I maximize another window in his background (used to open Firefox or Internet Explorer 8 so I can look for things in WoW Head, or when using WoW Cartographe), WoW slown down from 80 FPS to 5~10 FPS. I've to go back to my background application, minimize it, then minimize WoW and maximize it again so it goes back to work normally.
I'm running all this in a Intel Core2Quad Q6600 with 6 GB. of RAM DDR2-800 CL5 and a E-VGA GeForce 8800GTS, using updated Windows Update's
drivers.
Somebody got the same issue that I have?