IE7 window resize slow on a fast computer!?!

I'm fairly advanced when it comes to PC's (I built mine), and this has been stumping me for some time now. I have a pretty fast setup, and yet, when I run online tests like pcpitstop (just for ha-ha's), they say I should disable some appearance settings.
Well, I usually don't give much merit to 3rd party progs like that, esp tests run over the net, but I should be able to have EVERYTHING maxed on this PC with no problems showing up on any test! The ONLY time the UI lags is when I'm resizing my IE browser window...otherwise everything runs very fast, but I can't figure it out. It's silly that I can run games like HL2 and Quake4 w/literally every display setting maxed out, yet the stupid IE7 window lags like hell when I resize it! I know this seems like a very unimportant, trivial problem, but when I build a fast computer, I'm very picky about everything running fast and smooth. Here are my specs:

Win XP SP2 w/all updates
Pentium D 945 dual cores running @ 3.7Ghz
2GB Dual Channel Kingston HyperX RAM
Nvidia GeForce 7950GT (512MB GDDR3 Video RAM)
HD's: WD 40GB ATA, and WD 160 SATA

My GPU is a monster, and my CPU is pretty hefty too, so what would cause the lagging with the IE window? It's faster in Vista, but it's noticeable on that OS too. How can I correct this?