Cheap/Good computer?

I have 550 USD and I want to know what's the best I could do with it?
I've been thinking of maybe ordering one of these:
http://www.newegg.com/Product/Product.asp?Item=N82E16883107100
http://www.newegg.com/Product/Product.asp?Item=N82E16883103011R
http://www.newegg.com/Product/Product.asp?Item=N82E16883107103

Hmmmm.. Well, in about 7 weeks, I could get about 1,200 to 1,500-ish.. any ideas on what I could do then? I know building my own would be ideal, since that saves money.. But what should I look for?