Long ago, Innotek ported Connectix Virtual PC to OS/2. This product was lost when Microsoft bought Connectix. Microsoft continues to support Virtual PC on Windows.
The Microsoft Virtual PC Wiki offers more information about Virtual PC.
The hard drives supported by VPC tend to grow, but not shrink. To shrink them, you must first fill the unused space with zeros, then use VPC to compact the hard drive. This is the procedure I use to shrink my Windows 2000 virtual hard drives.
Microsoft has published quite a few security updates for Windows 2000. Unfortunately, not all of them are compatible with VPC. What follows is a list of updates to be avoided, and another list of those updates that are OK.
KB931784 - Crashes at the logon screen.
KB891861 - Crashes before the logon screen.
KB832483 - Won't apply.
KB840987 - Crashes at the logon screen. (Oct, 2008)