I have been using Virtual PC for various reasons around software development.  I find it very useful to maintain old development environments.  One of the big gotchas that I have run across is copying virtuals and attempting to use them on the network at the same time.  A copied virtual assumes the same machine identity so it ends up colliding with the original virtual on the network.  I know you can prepare a virtual image to prompt you for a new machine name when it first comes up but I have never looked into how it is done.  I found this article on using Virtual PC in a development environment.  It has a number of tips and tricks I have been using for a while but more importantly it has the instructions on how to make a virtual unique on the network.  http://coolthingoftheday.blogspot.com/2006/06/using-vpc-for-development-and.html