What can I do to get my computer to run Left 4 Dead (new valve game). I can't run it without lag on lowsetting?

Trust me, this game wont work. I have really similar specs, except i have a different processor + more RAM, and this game will run the same at ANY resolution/detail with an X3100. Left4Dead just isn't made for X3100, sorry to say it, I'm sad too ;w;