How does this setup look for a gaming rig [First ever build]

So just a heads up if this is a weird build or has issues, this is my first build and I really have no experience with computer parts so bare with me... Right now I really use my computer for internet surfing youtube, facebook, and a lot WoW. What I'm running is a stock HP computer that come loaded with Vista, I really can't tell you much more than that expect its like 4years old. What I'm looking for is to run WoW with better graphics and smoother than my current computer running the lowest settings at 10-15fps. This is a build I got after 2 days of research using Part Picker. I'm completely open to suggestions, but I'm hoping to not go much high in price than this current build.

CPU: Intel Core i5-3470 3.2GHz Quad Core Processor

Motherboard: MSI Z77A-G45 ATX LGA1155

Memory: Corsair XMS3 8GB (4x2GB)

Storage: Western Digital WD10EALX Internal Hard Drive 1TB 3.5" 7200RPM

Video Card: XFX Radeon HD 6850 1GB

Case: Cool Master HAF 922 (Black)

Power supply: Corsair CX 500W ATX 12V (80 Plus Bronze certified)

Optical Drive: Samsung SH-224BB DVD/CD Writer

As for the operating system, I know I want to get at least Windows 7 if not 8. I have seen people saying they use Windows 7 or 8 OEM, but I don't know what that is. Any help would be appreciated. Also, if any of you play WoW, how well do you think this set up run WoW?

Current build As is, with no OS is $751.10 US

Thanks, -Acbrown21