Virtual PC 2007 by Microsoft is a tool that lets you create and use one or multiple virtual machines on one computer. Each virtual machine would have its own OS. This setup offers you the flexibility to test different applications on various operating systems without having to spend more for additional hardware. The tool lets you keep the compatibility of custom and legacy apps when migrating to a completely new operating system. Virtual PC offers you a safety net to run important legacy apps on a temporary basis while IT professionals go ahead with their migration plan to the fresh OS.