I would honestly recommend completely wiping the old driver using the software I suggested, then installing the newest stable drivers completely fresh, that way you can be sure it's not the drivers.
1. Download the latest nvidia driver and save it to your machine, don't run it. (I'm suggesting that you download it before uninstalling the old drivers as it's no fun using the default VGA drivers to use the PC after the old drivers are uninstalled).
2. Download and run Display Driver Uninstaller. It'll prompt you at some point to boot into safe mode (optional, but I'd recommend it), run the program and restart the PC. There should be a tickbox relating to reinstalling the default Windows driver, make sure that it WON'T reinstall the driver automatically.
3. After reboot, install the new drivers you downloaded in step 1.
Chances are, if you still have an issue after this, the card is at fault. If you still get graphical glitches, remove the GTX660Ti and test the PC with the onboard graphics.
Do the graphical glitches appear in any other games? Are they related to any specific settings? If the glitches still appear when you're using the the integrated motherboard graphics then it might be indicative of some other software issue, possibly game specific (if that's the only game with a problem).
PC troubleshooting can be long winded sometimes, it's just a case of eliminating the possibilities, if you have any progress please let us know, we'd love to hear the outcome!