First time building, compatability

Just a tad imbalanced.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Pentium G620 2.6GHz Dual-Core Processor ($65.99 @ Newegg)
Motherboard: ASRock H61M-DGS Micro ATX LGA1155 Motherboard ($44.99 @ Amazon)
Memory: G.Skill Ripjaws Series 8GB (2 x 4GB) DDR3-1600 Memory ($38.98 @ Outlet PC)
Storage: Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive ($58.99 @ SuperBiiz)
Video Card: Sapphire Radeon HD 7850 1GB Video Card ($179.98 @ Newegg)
Case: Rosewill REDBONE ATX Mid Tower Case ($44.99 @ Amazon)
Power Supply: Corsair Builder 500W 80 PLUS Certified ATX12V Power Supply ($39.99 @ Newegg)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($17.89 @ Outlet PC)
Total: $481.80
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-11-29 19:04 EST-0500)

This is a slight mod of your build, but with a much stronger GPU, stronger processor, DVD drive (which you can remove) and more RAM. If you are unable to spend this much, you can go for a lesser video card.