What is the best PC for cheap price for gaming?

I am trying to look for a decent spec for a gaming desktop, but want to know what I'd need for a decent gaming desktop if I were to build one myself, for under $500.00

The spec's don't have to be all that great, If it works right. I play Perfect World International, and Second Life. So it has to be able to play both those games on Medium Graphic Settings.
I had a desktop back in 2008 that could play both on medium but i dont have that computer anymore unfortunately.

I was thinking of saving up money for next year; so I can buy one from Walmart; for a higher price with decent spec's but ya know how walmart is with their crappy spec's computers. eh!