[hikaricloud]

You're not going to be able to get both the GTX 260 and a quad core without skimping on parts way too much for 600 bucks. You could skimp through with an extra 100, but you know.

What resolution are you going to be gaming at? Do you really need that much power? Also, the x3 720 is just as fast as the x4 940 in gaming, since games don't really take advantage of quads yet.

EDIT: This is the best I can get without skimping.

Newegg.com - Computer Parts, PC Components, Laptop Computers, Digital Cameras and more!
Newegg.com - OCZ Reaper HPC Edition 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model OCZ2RPR800C44GK - Desktop Memory
Newegg.com - XFX GX260NADFF GeForce GTX 260 Core 216 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card - Desktop Graphics / Video Cards
Newegg.com - Seagate Barracuda 7200.11 ST3320613AS 320GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive - Internal Hard Drives
Newegg.com - Computer Parts, PC Components, Laptop Computers, Digital Cameras and more!
Newegg.com - LITE-ON Black 24X DVD+R 8X DVD+RW 8X DVD+R DL 22X DVD-R 6X DVD-RW SATA CD/DVD Burner - Bulk - CD / DVD Burners

Total comes to $675.88 after shipping, then you get 35 bucks back in MIRs.

This is about the best you're going to get for a decent quad core and a GTX 260. You can shave maybe 15 bucks by getting 2gb instead of 4gb, but that's really not worth it.