When I first got Vista I decided to check out hpow much RAM it was using up. While just sitting on my desktop it was eating up over 900 megs, compared to about 400 for my XP. I hear Windows 7 is comparable to XP as well. But at only 2 gigs to start with, that only leaves the game about a gig to use. Which is not really enough for optimal performance. Not only does he not have enough RAM, but his video card svcks and his CPU is also rather crappy. Yet he's trying to squeeze in these mods that puts all sorts of demands on a system. I have an 8800GT, which is far better than his 8400, but even I won't use QTP3. The compromises I have to make in performance just isn't worth it.
QTP3 beat up my 8800GT (awesome card by the way) and my 8850GT. It eats up 512MB really quickly. The rest of your visuals are fighting for attention.