Yeah that memory is fine, remember that DDR is double data rate, meaning that the memory speed on the label has to be multiplied by 2 to match the FSB. So for you to be running at 1:1 ratio you would need DDR2 800 and 1600FSB, now I would recommend that you definitely get those memory modules in case you want to overclock in the future.
At this time I'd be against getting 8GB of ram because it's really not necessary, only two games would make use of a bit more than 2GB, one is obviously Crysis (And not even so much... it has topped for me around 1.6GB or so) and the other is Assassin's Creed, but from what I hear this is due to a retarded engine from the developers. (Won't go into detail, but basically it loads the WHOLE huge .forge file on the ram even though it's making absolutely nothing with it.
What I'm trying to say is by the time you actually require 8GB in a few years you will already require to upgrade to a newer CPU, so there's no point on wasting $100 on RAM that you'll never use. I'm basing my opinion on your last post in which you stated that you are mostly a gamer, but have other apps that require a lot of power, IF by any chance you benefit from more than 4GB (Which I doubt), then disregard most of the above.
I'd wait a little IF you can to see the pricing on the 9800GTX (Basically an 8800GTS G92 overclocked that runs cooler), if the price gouging begins, then definitely go for the 8800GTS G92.
Corsair 620HX is a GREAT PSU and you will not be disappointed however if you're buying from the egg you might find it incredibly overpriced, so I'd recommend this equally good PSU for your system. (This one isn't modular however, so cable management will be slightly more difficult)
PC Power & Cooling S610EPS EPS12V 610W Continuous @ 40°C Power Supply 100 - 240 V UL, cUL, CE, CB, TUV - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16817703005
Other thing I'd like to comment on is the HDD, Raptors are not nearly as useful as people make them to be, the only REAL differences you'll see is maybe a 10-15 faster boot to the OS and 3-5 seconds loading in games, whereas for the same money you can get an HDD with 5 times as much storage space that will be competitive as far as speed goes.
Finally on the motherboard, I'll just recommend to you what I recommend to everyone going for an intel setup (I even got this board for my father's build).
GIGABYTE GA-P35-DS3L LGA 775 Intel P35 ATX All Solid Capacitor Intel Motherboard - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16813128059