Uh, why don't you just try out the Benchmark? It will test your PC with a few scenes rendered by the game engine. Click on the following link to see the instructions to download:
>Click me!<
The site also features a result measurement table. Be sure to disable all "special features" that your GFX-Card drivers may feature, try low res first.
Generally:
Benchmark runs = Game will run
Under 1500 points = You will have MAJOR problems playing, even with lowest graphic settings
1500-3500 points = Game will be playable at decent framerates with the right GFX-settings :-D
Over 3500 points = High res mode may be fun...
Over 4000 points = Have fun with all the bells and whistles
