Gaming PC's

So, I've been looking around for a gaming computer that doesn't destroy my wallet I'm thinking about buying a PS3..but honestly I suck at FPS' on anything besides a pc. Therefore, I've been looking online for some good computers and decided that Alienware is gay they charge waaaayyy to much and everyone else the computer is going to fail within 6 months. VisionMan looks like the best option, so i'm wondering what you guys would recommend I don't want complete crap so..lets say 500 to 900 dollars... Something that can run Cod 4 100% no problems. the laptop I have now can run it if I turn everything on the lowest settings. Besides textures for some reason I can keep them on Extra and it runs fine don't know whats up with that.
God bless!
God bless!