I was under the impression you could turn off or otherwise disable Prefetch, if not thats pretty lame. I had Vista for a month, and I can't speak for everyone, but my expieriences with it were attrocious. I am a gamer and it broke 3/4 of my games! The ones that worked were crippled!
That being said I was running a core duo laptop specs:
Core Duo @ 1.83 ghz
2 Gigs of ram @ 533mhz
Geforce 7900GS Go (only slightly overclocked once to test it)
120 Gig HDD @ 5400RPM (~50 gigs free when gaming)
1920 by 1200 flatpanel ( Was gaming at 1280 by 1024 or 1600 by 1200 depending on where I was (only using one monitor mind you))

My framerates were halved and loading was sluggish