Low performance on solid system.

Hey all, been awhile since I've posted here, but I'm some trouble figuring out why my buddy's system is getting such bad performance.

I got him the Orange Box thinking that his comp could easily handle it:

1440x900
4GB G.Skill DDR2-800
Q6600 2.4Ghz
NVIDIA 7900GS
Vista 32

When playing Team Fortress 2 at medium settings and 1280x800, multi core rendering enabled, AAx0/AFx2 we're getting about 5-30 FPS (30 FPS at spawn, ~5 while in a big fight, which blows). Vsync is also off.

So I figured, alright, the card doesn't like TF2 much, so then I go into Half Life 2 and it can barely play the game on high and still get 25-35 during normal play. Same with Portal.

I don't get it, when I had that 7900GS in my E8400 rig (other specs were the same) I was getting 30-40 FPS on high settings at the same resolution. Clearly there's something wrong here. Drivers are up to date, and I doubt a defrag will make a 30 FPS difference that this game evidently needs... and everyone knows how well Source games run on decent CPUs... I just don't get it.

It's been a while since I've tweaked graphics card stuff, but I just can't figure it out. I know that the 7900GS is a pretty outdated card, but for the Orange Box, it should be more then enough.

Thanks.