i wouldnt get the quad for gaming unless ur going to oc. the clock on it is a little to low. get the e8200 or higher.
4ddr@800mhz like spac13 said. get the 4850 since u seem to be on a budget 9600gt not a great card to play games like crysis. And hopefully the os u have is 64bit.
I agree, go for 800MHz DDR2, an E8400 and a HD4850. As for the mobo, a P43 or P45 will do. Don't forget about the PSU, get at least a solid 500W.
+1 here if you want to play Crysis.
The original parts you had listed are very marginal gaming parts by the latest standards. If you do not overclock the Q6600 to 3.0ghz, it is not favored as a heavy gaming processor. (at least not nearly as good as the dual core Wolfdales, like the 8400)
i would say that you dont have to worry about your processor, however your card is not that great, as an above poster said, get a 8800series card or a 9800 series card. Also your ram is sort of slow, preferably ddr2 and 800mhz+ at least if you want to run some of the good games like crysis which chew up ram more then you can imagine.