I know you like DFI motherboards and they are pretty good. You linked it before and this is a good one:
DFI LANPARTY UT nF4 SLI-DR Expert Socket 939 NVIDIA nForce4 SLI ATX AMD Motherboard - Retail
It's SLi ready. YOu have to make sure you read the manual carefully. You can use one video card if you don't have the money for two cards. It will work perfectly. Just make sure to follow the manual as to which port to install the single video card in. I think it might be the very first slot, then again, it could be the second PCI-e x16 slot. The manual will tell you all that info. Good stuff.
Get the dual core CPU if you can or go with a single Athlon 64 4000+ San Diego.
AMD Athlon 64 4000+ San Diego 1GHz FSB 1MB L2 Cache Socket 939 Processor - Retail
This one's on sale for 8 hours only:
AMD Athlon 64 X2 4200+ Manchester 1GHz FSB 2 x 512KB L2 Cache Socket 939 Dual Core Processor - Retail
I prefer the Toledo core, but it adds to the cost.
This is the cheapest RAM I would go with:
OCZ Gold Series 1GB (2 x 512MB) 184-Pin DDR SDRAM Unbuffered DDR 400 (PC 3200) Dual Channel Kit System Memory - Retail