It might be worth trying hdtach, that'll give you a readout of speed across the drive and cpu usage, if speeds are all over the place and cpu usage is over the top it might hint at a problem.
I wouldn't necessarily class Vista and Windows 7 as different OS on the driver front either, if the chipset manufacturer did iffy Vista drivers they are probably the same ones on 7 too (though I assume Microsoft can still install some default drivers). I deleted my XP and installed 7 on my main machine and had some stalling problems and media player was very ropey. I reinstalled in 32bit and it seemed better, but still prone to odd lockups etc. I had various bits of software that it didn't like and so went back to XP.
Might be worth saying what motherboard/chipset you have.