About Windows Installer, the .NET Framework, and Visual Studio.
Earlier today, Microsoft announced that Virtual PC 2004 SP1 is now free to download, and that Virtual PC 2007 will be free when released. Earlier this year Virtual Server 2005 R2 was made available for free download as well.
Virtualization is great when testing Windows Installer packages and patches for installation and maintenance scenarios. I've been using Virtual PC 2004 SP1 at home since it was available for testing private projects, such as my shell extensions which can be a pain to test on your development machine. I use Virtual Server 2005 R2 at work to test installation packages and our patches so that I can use different versions of a unreleased patch or test patches without always changing the package code, which makes it easier to test obsolescence.
In both cases, I've enable undo disks which allows me to have a base platform and then install anything else on a separate, virtual hard disk. When I'm finished, I simply discard the undo disks and I can be back up and running in the base platform in almost no time. It saves time and hassle when debugging processes or testing packages, which avoids the possibility of loading an existing patch with older changes.