Microsoft Virtual PC 2007

Virtual PC 2007 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

Virtual PC lets you create separate virtual machines on your Windows desktop, each of which virtualizes the hardware of a complete physical computer. Use virtual machines to run operating systems such as MS-DOS, Windows, and OS/2. You can run multiple operating systems at once on a single physical computer and switch between them as easily as switching applications—instantly, with a mouse click. Virtual PC is perfect for any scenario in which you need to support multiple operating systems, whether you use it for tech support, legacy application support, training, or just for consolidating physical computers.

And what makes it better than any other similar programs, Microsoft Virtual PC 2007 is free ! and that means you don't have to pay anything in order to use this program

Grab it from here, the filesize for the 32 Bit and 64 Bit version of Virtual PC2007 are 30.4MB and 30.5MB respectively