BleepingComputer.com: Sims 2 Drags When Playing.

I installed the Sims 2 and some expansion packs on my PC for my sister. She's been complaining about how slow it is, and how much faster it is on our other computer. I started it up and right after it loads it just drags along. I've downloaded the patches and I've set the graphics settings as low as possible and still goes extremely slow. I don't think it's the computer, because it's more than powerful enough to run the game, though I don't know why the other computer runs it faster. Mine: XFX nVidia GeForce 8600GT XXX 256MB Overclocked, Core 2 Duo E4500 overclocked, while the other computer: Pentium 4 processor, Palit nVidia FX5600. I'm starting to blame Vista on this one. And it's only this game that goes that slow, Warcraft, Flight Simulator X (on full graphics settings), and SWAT 4 run incredibly. How can i get this game to run on here without slowing down?

Thanks,
n0data