Good enough for 2006 gaming...
I've got the same model; Valve games seem to work great, as I've had Half-Life 2, Counter-Strike: Source running at 60FPS at full settings, and TF2 and Portal 2 running at medium-high settings at around 30FPS-40FPS.
I wouldn't try running games like BF3 and Crysis on it, but it does fine for the games mentioned above and most of the App Store games.
8Gb the minimum for gaming ? You must be joking.
Btw, you forgot 2Gb of video RAM, 10Tb HD for all those save games and 30" display at the very least (you don't want to be staring at a tiny screen, do you now...)
i too would recommend 8GB for gaming. 4GB is not enough for me for some games, ie crysis 64bit.