While not 100% related to Tabula Rasa, hardware and software updates can very easily affect how your game runs. Nvidia has put out Release 169 for both Windows XP and Vista to provide Forceware for the Geforce 6, 7, and 8 series cards and address several issues. That pretty much means everyone (unless you own an ATI card) so make sure to stop by Nvidia's update page and download them.