After reading my post on how I use virtual machines, Andrew Connell pointed me to an article he wrote about his extensive use of Virtual PC, including how he uses Differencing disks to his advantage. He also says he doesn't see the huge differencing disks that I'd heard about in the past. I'm now rethinking my plan, and when I update my base image to have Visual Studio 2005, I may give it a try.My biggest hang up with using differencing disks wasn't the size - I really do find it hard to believe...