If you have the machine power for it, though, there is a method that is actually supported by Microsoft to accomplish this. It employs virtualization which is becoming increasingly popular in the computing world. It is useful for two particular applications: to make server environment installations independent of the host operating system and hardware and to allow multiple operating systems to coexist on the same hardware without the need for partitioning storage devices.

In 2003, Microsoft bought out a company called Connectix which specialized in virtualization software, one of their main products being Virtual PC. Microsoft subsequently released a rebranded version of VPC as a free download.

Once the need to test applications on IE6 and IE7 for cross-compatibility was realized, Microsoft also began sporadically releasing a freely downloadable series of up-to-date Windows XP images with IE6 pre-installed and expiration dates after which the images would no longer function. The latest image is set to expire in early June 2008.

With Microsoft pushing adoption of Windows Vista and IE7, it’s uncertain as to whether or not Microsoft will continue releasing these VPC images. However, it does appear that Microsoft plans to continue developing Virtual PC. Therefore, if you have an extra Windows XP license to spare, this arrangement is a nice and relatively lightweight solution to making IE6 and IE7 available for testing on the same machine.