Advice on a 500 gaming build excluding a video card

Hi can someone give me some mock ups on a ballpark 500 dollar gaming build excluding the video card(s). I would prefer a potential crossfire/sli setup so a good motherboard and psu are probably the top priorities along with a case that can fit two cards, as well as a processor and ram that can properly drive the setup all while keeping a slim budget in mind this could be tough, but there are a lot of packages and mail in rebates going around so please post your best results, the video card that Iwill be purchasing to go along with this rig will be of 5850 level or higher, unless of course a cheaper, faster sli/crossfire configuration can be achieved. DX11 means very little to me right now and I am more concerned with getting a proper motherboard/psu with the potential to upgrade the video card(s) in the future. Thanks for your help, I really appreciate it.

here is my current rig that i am hoping to significantly improve performance upon:
AMD athlon II X2 240 (2.8), 6 gigabytes of 667mhz ddr2, 600w cheapo psu, gigabyte GA-MA785GM-US2H, Hitachi 1 tb harddrive. 7200rpm, 6 120 mm case fans, Thermaltake r1 cpu cooler, BFG gtx 260 core 216. Lite-on DVD drive. Case: Thermaltake V3

I am selling this comp to raise some money for my new build, also I will be gaming mainly at 1650X1024 or in some instances 1920X1080.

Any suggestions are very greatly appreciated