Like I said above, it's really best to just start with build you own.
You won't have to deal with upgrading hardware just to upgrade other hardware down the road. lol
(did that make sense?)
Any who, the system I built above will be faster then any prebuilt you get in your price range. Plus, it comes with the new Call of Duty game.
One thing I did forget is a operating system though, so make sure you factor that in.