i got the same probleme and my pc is better then his the only thing that is working for me right now is using prosses laso running every thing on 2 core and only the game on the other 2 and putting it priority up to real time highest!!

i dont sugest this if you dont have a 4core

ps my spec are
4core 3.0 ghz
285GTX
my monitor can go up to 120 refresh rate
and XP 64 cause it only uses 512 mb to run and vista take 1G

anyways that what i did