I assume you realize it's "in-store only"?
Also, not sure what other parts you have to buy, but by the time you pay about $100 for Windows (unless getting Linux) you're probably better off getting a cheap laptop for $350 which you can still hookup to a monitor.
*FYI, some people are under the mistake assumption that they can take a Windows disc they already installed or just the entire hard drive from another PC and use it with a new motherboard. Nope. That only applies to FULL versions which few people have.
Just an example:http://www.frys.com/product/7167982?site=sr:SEARCH:MAIN_RSLT_PG