Some time ago Cisco's IOU was leaked out to the web. I was able to get a copy (don't ask where, I won't help you) and have managed to get it set up on a spare box at home. There are a couple of really good tutorials on the Web that explain how to get it set up and working and how to build a lab topology. I've built two topologies so far that I use to lab things up when needed, and I'd like to share the first with you now.