I don't have matching HW to try but on vista 64/ie8b2 in compat mode and dual core with realtek chip I've not had such problem.
Just to verify, you have tried other browsers incl IE7 and with no new drivers installed in between with different result? Can you change the amount of cores in use from BIOS? I can't remember if you could boot Vista with a generic "vga driver" rather than accelerated one but I'd try that too to see if there's any effect.
Mmm, also FF is skipping/popping when scrolling, so it is not a browser issue. I am trying with all sorts of drivers, lets see if I ge lucky...