4GB of RAM and using a GeForce 8800. Might be time to upgrade.
Not really what I asked for but it's enough to tell you that your GPU is not capable of handling it.
Also, more ram never hurts, its also pretty cheap.
Assuming one has a 64-bit OS, of course. Also, there's a limit to where it's actually useful if you're not doing dev work, designing, or other memory intensive stuff. For day to day usage, including gaming, 6 - 8 GB is a sweet spot.
Also, this really should be here: http://www.gamesas.com/forum/180-pc/