The Best Buy link is a nice system, but I would go to Velocity Micro's own site and price out a system there instead. I'm using a VM system for my additional boxed characters (2 at the moment, might add 2 more). I am considering replacing that box with a quad-core system, but first I want to see if the current one can handle 4 accounts at once.

Then again if your intention is to run 5 accounts on 5 separate boxes, the quad-core system is probably overkill, look for a system with more modest CPU and GPU options and 2GB RAM instead. For the secondary boxes I'd go to Best Buy or Circuit City and see what they have in the price range you are after. They often have decent Gateway or Dell systems for a very nice price ($350-700).