Microsoft releases free Windows XP Virtual PC images
The images should come in handy for anyone running Windows Vista who wants to see how their web page look in Internet Explorer under Windows XP. Of course, you could also run the disc image inside of Virtual PC if you want to try installing new software without risking any damage to your host operating system.
The disc images are under 500MB and expire on August 17th, 2007. The images are pre-activated, and include no product keys, so you can't grab a key from these images and use it to activate a full version of Windows XP.
These images will not work under Virtual PC for Mac.