Late reply, but will reply anyway..
8600 GT is better than 9500 GT... Go to the store and tell that to them if they didn't know it..
WHAT ARE THE REST OF YOUR COMPONENTS IN YOUR PC? No matter what the guy in the store says, if you have a problem, you tell the components to us IF you want any help..
Try this too: Un-install drivers with (example driversweeper) and install newest graphics drivers (no, uninstalling it from control panel or nvidia's own uninstall won't uninstall them "totally")