Oh boy..... Linux? What are you all people suggesting! That is so uncool for gaming. No No No... You need Windows and you need serious deals on components and then you can get a good computer built by yourself of course.
If you are planning on going with AMD, then you can get the FX-6100 Six Core Processor, 3.30GHz (3.90GHz Max Turbo), Socket AM3+ for around $160, you can always get a much cheaper CPU but you know...
Then for the Motherboard, you can get nearly any $50 dollar motherboard and i recommend going with ASUS just because they are the best and give the customer good product support.
Then you get the memory for around $50 and that's 8GB DDR3 most likely with cooling, depends on which brand you buy.
You can get a really nice Case with two amazing fans coming with it, the Antec Three Hundred Mid Tower Case, Newegg has it, I bought one recently around $70 for a client's computer and then they dropped the price to like $40
I think that you've got the Power Supply, Disk Storage and CD Drives covered but if you need suggestions, I can help you with that aswell. As far as the Windows goes, give me a message and I can point you in the right direction on getting a Genuine product key for an insane price.... Although that method is technically possible, the legality of it is highly questionable.--hym, If Money is an issue at this time.