Rambler,
Just to let you know my ‘inner junior-highschool kid’ hates your guts for having access to such gear and opportunities to learn this stuff at so young an age! Looking back though, I don’t know how much good a desktop computer would have done me during the ‘Ice Age’….
Seriously though, check out this unit from TD’s Systemax line. Price after shipping is on the low-end of what you want to pay, but you get a good processor and a good deal of RAM. The GPU in it is not shabby and you get an upgrade from Vista to Win7 for the price of shipping. Not bad for a starter rig and it’s less than your quoted price of $650.
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4396007&Sku=SYX-2008
