CORSAIR CMPSU-650TX 650W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS Certified Active PFC Compatible with Core i7 Power Supply - Retail
http://www.newegg.com/Product/Prod [...] &Tpk=650tx ($89.99 w/ $10 MIR)
Intel Core i5 750 Lynnfield 2.66GHz 8MB L3 Cache LGA 1156 95W Quad-Core Processor - Retail
http://www.newegg.com/Product/Prod [...] -_-Product ($206.99)
GIGABYTE GA-P55-UD3R LGA 1156 Intel P55 ATX Intel Motherboard - Retail
http://www.newegg.com/Product/Prod [...] 6813128401 ($139.99)
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Desktop Memory Model F3-10666CL7D-4GBRH - Retail
http://www.newegg.com/Product/Prod [...] 6820231276 ($89.99)
SAMSUNG Spinpoint F3 HD502HJ 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive - OEM
http://www.newegg.com/Product/Prod [...] -_-Product ($49.99)
SAMSUNG Black 22X DVD+R 8X DVD+RW 16X DVD-ROM 48X CD-ROM 2MB Cache SATA DVD Burner - OEM
http://www.newegg.com/Product/Prod [...] 6827151187 ($30.99)
Total: $607.94
Now here the problem, you want to purchase the video card seperately, which is fine, but this build does not have integrated graphics. The HD4870 1GB is a great choice for you, but its ~$150.00. You could get something like a HD4350 to hold you off until you buy the nicer GPU (Cheap temporary option), or go ahead and spend the money and get everything now. I would never use that PSU you have, and would probably just throw it away, it only stands the chance to ruin this new hardware you are adding.
Temporary GPU: GIGABYTE GV-R435OC-512I Radeon HD 4350 512MB 64-bit GDDR2 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Low Profile Ready Video Card - Retail*
http://www.newegg.com/Product/Prod [...] 6814125251 ($24.99 w/ $10 MIR)
*Do not expect to play games on this, save for older one, this will merely let you use the computer until you get something nice
Total: $632.93
GPU: SAPPHIRE Vapor-X Radeon HD 4870 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Prod [...] -_-Product ($159.99)
Better GPU (~$25 more): SAPPHIRE 100269HDMI Radeon HD 4890 1GB 256-bit GDDR5 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card - Retail
http://www.newegg.com/Product/Prod [...] -_-Product ($174.99 w/ $20 MIR)
I would say go with the temporary GPU option, and then get the HD4890 when you plan on buying a good GPU.