Mr Optimistic

That sounds familiar. Happens from time to time, latest I had was with Doom 3. I changed from m/b sound to a pci card and upgraded the graphics card and now problem has gone. Your graphics card is a lot behind the pace.

Not much help but I have run Sims 2 on 9600 Pro and 9800SE cards without problems so its not intrinsic to the cards or the 4.9 drivers that I can see. I presume the 'dxdiag' checks all complete/show no problems ?