help in buying gaming computer

I have been trying to educate myself on specs needed for a decent gaming computer. Its a little overwhelming and am asking for help in how to go about this. So far i understand I need a quad core processor, 8gigs of ram and a dedicated video card. I can not spend more than $550. I would rather find a way to pick the specs I want and have someone build it for me, but I don't know where to go. I have also checked out CybertronPC and have no problem buying one of these, but I want to make sure the video card is decent. I don't need max settings, but maybe medium to high.

Any help appreciated.

I didn't find the right solution from the Internet.

reference:
www.cnet.com/forums/discussions/help-in-buying-gaming-computer/
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Thanks!