I need to upgrade as well. I have the same processor and 4gigs of ram with Vista64. Its just not enough power to run 5 for me. I have been looking at the following...

Intel Core 2 Quad Q9300 Yorkfield 2.5GHz LGA 775 95W Quad-Core Processor Model EU80580PJ0606M - OEM
SAPPHIRE Toxic 100225TXSR Radeon HD 3870 512MB 256-bit GDDR4 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail (This would be my second Toxic card. Right now I have one of these with a ATI x1950xtx but this toxic card is just too nice. I am going to ebay my 1950 and put another toxic in.)
CORSAIR XMS2 DHX 4GB(2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model TWIN2X4096-6400C4DHX - Retail X 2 for 8gigs of ram.

That toxic video card is water cooled and only takes up one slot. Right now my 1950 has one of those huge bulky fans that take up two slots. The big issue now is with this new hardware should I just bite the bullet and upgrade my motherboard? I was looking at the Asus Maxiumus Formula motherboard which is about $250. I cant decide if I want to get all this stuff. I would be gutting my current pc and spending nearly $1000. I cant decide! All I know is the Core 2 Duo 6600 and 4meg ram with Vista 64 is just not enough to run 5 wows.