I pulled down Microsoft's VPC 2007, which is free, a few weeks ago and have been using it on my Windows XP workstation and laptop. I even have a VPC machine with Vista and Office 2007.
I setup the VPC machine with Vista and then created a copy of the VPC to test drive. This enables me to play with it, and even break it with no issues. If I mess it up I just make another copy of my master VPC and go at it again. This is great for development and testing.
I even got the Ubuntu Desktop on a VPC machine thanks to a blog post from Arcane entitled Installing Ubuntu 6.10 on Virtual PC 2007 Step by Step.