I read about the Altiris Software Virtualization Solution (use bugmenot.com for a password, there is even a Firefox extension to make it easier) from LifeHacker a while ago and I have really enjoyed using it.
SVS lets me install software and then uninstall it easily. It installs them into virtual data layers so that when it comes time to uninstall then the entire layer is removed without any of the junk being left behind. You have to be careful because some stuff you may want will disappear as well. I installed Opera 9 Beta to try out some of the new features, but when I deactivated the layer containing Opera I lost the files I downloaded as well. Reactivating the layer brought them back so I copied them somewhere else and was able to keep them when the layer was removed again.
This will let you easily install multiple versions of a particular program and run them separately without interference. It lets you install programs that you rarely use and have them completely out of your way when you don’t want them around.
Altiris has a lot of community generated add-ons for this and other programs so there feels like there is a lot of life in it for the future.
It does require free registration to use the software, but it is not intrusive.
UPDATE: Scott Jones from Altiris replied in the comments (which don’t always show up in feedreaders) with some alternative locations to download SVS. You may also be interested in this selection of prepackaged virtualized layers.
We know that not everyone wants to register to get our software, so we provide several download options. The list is here: http://juice.altiris.com/node/86. Share and enjoy!