Updated

Microsoft said this week that it will make its Virtual PC software free — not just the older Virtual PC 2004 version, but its upcoming software for Vista, too.

Users can download the Virtual PC 2004 Service Pack 1 software from the Microsoft Web site. The software allows users to run multiple instances of operating systems on a single computer, allowing users to test a new development environment or simply try out a new configuration without changing the underlying OS.

Microsoft's Virtual PC 2004 SP1 software requires Windows 2000 Professional SP4, Windows XP Professional or later, and Windows XP Tablet PC Edition or later.

Microsoft also said that its upcoming Virtual PC 2007 for Windows Vista PCs will also be released free of charge. Microsoft has not released an estimated ship date for that piece of software, however.

[Microsoft has not made the Apple Macintosh version of Virtual PC free. That application allows PowerPC-based Macs to run Windows or other PC-based operating systems in an emulation window. It does not work on Intel-based Macs, which can run Windows natively.]