Well I think its possible, but no way through a USB 2.0.
Graphics need alot more bandwidth than usb 2 could provide.
I mean, I've heard of people using external gpus, but im not sure its the easyest/cheapest/smartest option.
Bottom line, to increase performance no. Not really. There are some ridiculous expresscard options but they are expensive and very limited performance. There's just not an interface for this (besides thunderbolt on a few very new laptops).
There ARE some USB2.0 devices you can run another monitor using but they are just to add another monitor for productivity. Not for gaming. performance would go down since there would be another monitor to drive