I never had problems installing sp2 on my a64. even from updating my existing installation to a fresh install with sp2 integrated.
Do you try to update while overclocked? do you have any antivirus running while you try to update? Did youtry to update a fresh install or simply updating in safe mode?What if you disable all onboard stuff and remove your sound card and non necessary for now card in your machine?
-Always put the blame on you first, then on the hardware !!!