AMD A10-5800K Trinity 3.8GHz (4.2GHz Turbo) Socket FM2 100W Quad-Core Desktop APUhttp://www.newegg.com/Product/Product.aspx?Item=N82E16819113280
Kingston HyperX Blu 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600http://www.newegg.com/Product/Product.aspx?Item=N82E16820104203
GIGABYTE GA-F2A55M-HD2 FM2 AMD A55 (Hudson D2) HDMI Micro ATX AMD Motherboard http://www.newegg.com/Product/Product.aspx?Item=N82E16813128571
CORSAIR Builder Series CX430 V2 (CMPSU-430CXV2) 430W ATX12V v2.3 80 PLUS BRONZE Certified Active PFC Power Supply http://www.newegg.com/Product/Product.aspx?Item=N82E16817139026
MSI R6670-MD1GD3 Radeon HD 6670 1GB 128-bit DDR3 PCI Express 2.1 x16 HDCP Ready Video Card http://www.newegg.com/Product/Product.aspx?Item=N82E16814127666
COOLER MASTER Elite 311 RC-311B-RWN1 Red Steel / Plastic ATX Mid Tower Computer Case http://www.newegg.com/Product/Product.aspx?Item=N82E16811119249
TOTAL - $377.44 there are $25 in mail in rebates too which would make it $352
I added a case as your old one may not have standard mounts for the new mobo. You need the RAM too as your old one wont be DDR3. The APU will hybrid crossfire with the graphics card. I assume your current DVD and HDD are SATA so you can resue them if they are not you will need to replace them too. Also this does not include windows that would add cost if you need it.
You wont set the world on fire with this but it will do for basic gaming.