I've installed and used both VMWare and Virtual PC on my tablet. VPC has one key advantage: It lets the guest OS use the right drivers for your hardware. VMWare installs its own drivers for things like display and network. In my case, VMWare's virtualized drivers caused two problems: The guest OS could not connect to the network using the host's wireless connection. This is meant I always had to be plugged in to an ethernet for the guest to be connected - an inconvenience more than a real problem. The second, more serious, issue was going into full screen. VMWare let me choose 640x480 or 1024x768. Going into full screen with the latter resolution caused my tablet's display to go into vertical (portrait) mode. I tried everything I could think of to put it back to landscape but had no success. This is a real issue since, needless to say, using VS .NET in 640x480 is a real challenge. VPC has none of these problems. I can use my wireless network from the guest OS and I can choose from 640x480, 800x600, and 1024x768 all in full screen mode. Although there's one slight problem in VPC: When using the wireless network, the guest OS cannot ping the host OS. I can live with that.
Next I want to install Longhorn in a VPC on my tablet. I don't even know if VPC supports Longhorn, stay tuned.