From Microsoft's IE Blog:
IE Blog wrote:IE6 and IE7 Running on a Single Machine
Many of you have asked how to run IE6 and IE7 in a side by side environment. As Chris Wilson blogged about early this year, itâ€™s unfortunately not so easy to do. There are workarounds, but they are unsupported and donâ€™t necessarily work the same way as IE6 or IE7 would work when installed properly. As Chris said, the best way to use multiple versions of IE on one machine is via virtualization. Microsoft has recently made Virtual PC 2004 a free download; weâ€™ve taken advantage of that by releasing a VPC virtual machine image containing a pre-activated Windows XP SP2, IE6 and the IE7 Readiness Toolkit to help facilitate your testing and development. The image is time bombed and will no longer function after April 1, 2007. We hope to continue to provide these images in the future as a service to web developers.
Now you can install IE7 on your main machine for development, and get all the advantages of IE7, like the RSS platform, native XMLHTTP stack, and improved security, while still running IE6 simultaneously in the VPC on the same computer. Most importantly, you donâ€™t even have to buy an additional Windows license. The VPC image runs in a virtual machine that offers all of the functionality of a full IE6 installation without giving it any access to its host machineâ€™s hard drive, registry, etc. You can make as many modifications as you want to the virtual machine without affecting your host installation at all.
Included in the VPC image are:
* Windows XP Professional SP2 + high-priority fixes through November 2006
* Internet Explorer 6.0
* Internet Explorer 7 Readiness Toolkit 2.0
While weâ€™ve released a VPC image today with Windows XP SP2, weâ€™re also investigating creating other VPC images, for example IE5, IE5.5, IE6 and IE6 SP1, as well as versions of IE on different language operating systems.
Get more information on Virtual PC 2004
Download Virtual PC 2004
Download the Internet Explorer 6 Testing VPC Image
One more note - VPC 2004 doesnâ€™t run on Windows Vista, but this image will work fine with VPC 2007, which is in beta now. You can get this free beta via Connect.
I'll be sure to download my copy of this image ASAP!