Testing with different configurations is an integral part of the QA process, but time and energy is consumed configuring and managing these environments. Ben Waldron has written an article demonstrates how the Virtual Server COM API can be used to create an automated application testing environment using Virtual Server 2005. It improves developer productivity by simplifying the provisioning and management of testing environments.
If your application runs on Windows, you need to take a look at using Virtual PC and Virtual Server 2005 as integral part of your QA environments.