A long upgrade help post

I just got a new PC that was compleatly built out of mostly low end cheap stuff which I had no choice in. Now I have to get it up tothe the level that I like with any PC. I have already got a new EVGA 8800GT SC so now I have 2 major things I want upgraded. I like to check before I buy so here it goes.

Right now I have 2GB of 667MHz non dual channel DDR2 RAM for my PC. I want to get some new stuff and its either I geta new pair of 1GB800MHz Dual Channel DDR2 RAM or I get a new set of 667MHz Dual Channel DDR2 RAM and am able to keep my old RAM because it operates at the same speeds. So basiclyis 4GB of 667MHz or 2GB of 800MHz better? I am really tired of getting the "Your computer is low on memory" windows pop up when I play Crysis so will faster RAM fix that at all or just more GB? These are my choices for the 800MHz DDR2 RAM and the 667MHz DDR2 RAM.

My CPU right now is an Intel Core2 Duo 6450 2.13Ghz. This isn't really cutting it for me with all the stuff that I do so I am looking at either the Q6600 2.4GHz Quad Core or an E6600 2.4GHzDual Core. So really is it worth the extra $30 for a quad or should I just get the dual?

One last thing. Can I run a 8800GT SC, Audigy sound card, the quad core processor, either 4GB or 2GB of RAM, a320GB SATA HD and 2 DVD drives with a 500W PSU? Or what should I step it up to?

well wat OS are you using? if its Vista 64bit i can read upto 4gb of RAM but the 32 bits can only read a max 3gb or sumthing like thateven if you have 4gb of RAM, also i got 2gb RAM @ 800mhz and i have no prob wif crysis

and i got my Q6600 OC'ed to 3.2 ghz, its really good and i heard ppl can get up to 3.5ghz+

well wat OS are you using? if its Vista 64bit i can read upto 4gb of RAM but the 32 bits can only read a max 3gb or sumthing like thateven if you have 4gb of RAM, also i got 2gb RAM @ 800mhz and i have no prob wif crysis

and i got my Q6600 OC'ed to 3.2 ghz, its really good and i heard ppl can get up to 3.5ghz+