Might I suggest that you either buy a used gaming PC or save a hundred or so more dollars then do the build. It's very hard to build a gaming PC for that much when you include the price of the operating system which is usually $100.
Do you need an operating system, or any peripherals to go w/ that budget? If so, you should just continue saving up. But if not, what games do you intend on playing?
Here's a build for $330 then you could pick up a copy of Windows 7 on ebay for $70 to $80, keeping you within your budget. It's not the greatest build but games will be playable and you could always upgrade in the future.