I run 4 copies on my laptop currently, get between 50 and 60 fps on each instance (granted everything is set to lowest).

Video/Graphics Card: Dual 512MB NVidia® GeForce™ Go 7950 GTX - SLI Enabled (going to upgrade it to the dual 8799gt's soon)

Processor: Intel® Core™ 2 Duo Processor T7400 2.16GHz 4MB Cache 667MHz FSB

Ram: 4 gb