Microsoft is now offering its Virtual PC 2004 SP1 product for free. See:
Microsoft Virtual PC 2004 Service Pack Virtual PC 2004 Service Pack 1 (SP1) is a powerful software virtualization solution that allows you to run multiple PC-based operating systems simultaneously on one workstation, providing a safety net to maintain compatibility with legacy applications while you migrate to a new operating system. It also saves reconfiguration time, so your support, development, and training staff can work more efficiently.
Microsoft Virtual PC 2004 Systems Requirements
Virtual PC 2004 SP1 runs on: Windows 2000 Professional SP4, Windows XP Professional or later, and Windows XP Tablet PC Edition or later.