I would have to say it's a driver issue, I had the very same thing happen to me when I installed the latest Nvidia 91.31 drivers (Beta) from Nzone. every time I switched views I had a massive drop in FPS I then went back to my much loved and tested Force ware 84.66 drivers from Guru of 3D..... You can get the Jelly belly cert drivers or I go for the Force ware ultra "Sedona" 84.66. The Nvidia 84 set of drivers are well loved in the gaming/overclocking community for there stability. Now if you have trouble with these drivers then pop on over to Tweaks R us and get there XTremeG 84.56 v3, another great modified and STABLE driver well suited to Geforce 6600GT cards
here are your links :
http://downloads.guru3d.com/download.php?id=2 this is for the "sedona"
And go here :
http://www.tweaksrus.com/index.php?o...127&Itemid=41/
This will take you straight to the Extreme downloads page....
Remember if you are going to install new drivers you must get a good cleaner to get all the left over reg settings that do not disappear when you un-install your previous driver and can recommend one very cool program that's free called Drive cleaner pro get it from here :
http://downloads.guru3d.com/download.php?id=8.
As a quick guide un-install your current drivers using the control panel Add/Remove, once you have rebooted run Drive cleaner pro setting the cleaner for Nvidia once that has cleaned out all that was left over then install your new driver, CAUTION if you are going to install the 84.66 Sedona when it asks you do you want it to clean your files say NO just continue with your install as you have already cleaned out any residing nvidia reg edits...Hope this helps.....and if these don't work try any of the other of the driver sets at both sites..... BOY do not go anywhere near the new 91XX drivers as they are totally crap and at the moment have issues with AA properly working above 2X !!!!!
Deep Six