Is there a PC equivalent to the Mac Mini? I'm looking for a cheap PC to run Windows strictly for testing designs. It doesn't need to be fast, it just needs to be inexpensive, with the smallest footprint possible.

I've been using Virtual PC for the Mac for a long time now. It's convenient and works fine, but it's dreadfully slow -- not to mention the version I have isn't compatible on newer, dual processor G5s (where I'm sure it'd run faster). So, my other option is: set up a bare bones Windows machine for testing without spending a ton of money and taking up a lot of desk space. Share with us your secrets.