Ack..I should of payed attention to the memory segment...If you aren't overclocking, any memory will do, I'd suggest just getting a cheaper set of 2x1 ddr-2 800 modules so you can focus funds onto cpu/gpu. You'll see more of a performance improvement on cpu/gpu compared to ram...Corsair has lost a lot of following after they cheaped out replacing their Micron D9GMH IC's in their dominator line for lower quality chips....
Newegg.com - BUFFALO Firestix 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Desktop Memory
This should do you fine, and checked for compatibility...^_^
BTW...I took the courtesy of making you a list, Unfortunately I didn't include the OS, which would put you overbudget by around 50-60 for a OEM copy (tried to stay below 500, but would help if you stated yours =P)...But it's still very similar to your system, just a better quality board, good ram at a great price, and a better graphics card...Much more capable system. I left out case and power supply because you didn't mention any, do you have them already?..If so, brand/model?..
https://secure.newegg.com/NewVersion...hListTitle=Mel
There's the list, I dropped the Nvidia chipset, why pick up a nvidia chipset?..It was a older one to boot, you can get a nice quality AMD chipset for the same price. If you want to go even cheaper, you can pick up a nice 770 chipset that can save you an additional 10 bucks...The board selected is also AM2+, newer platform, better then going with the nvidia chipset board. This one also sports a full solid capacitor design ^_^...
Firestix modules are great for the price, even 4-4-4-12 cas timings..Which are very helpful for AMD processors with hyper transport and their IMC...Lower timings are more important for AMD based platforms compared to intel.
hopefully this helps a bit, the 9600 GT will give you EXCELLENT performance, worlds above a 8600Gt...which is just old technology =(....and was scrutinized on launch for not being worth the money as a midrange card.