Altiris used to offer this software free for personal/noncommercial use. I was surprised to discover that this was still available after Symantec bought them out, and figured some of the computer gurus here might get a little use out of it.

Go to the following link:

Download link at Symantec , under Trialware click on the Software Virtualization Solution link. Unless you have an account on Symantec's website, you'll have to create one at this point or login (if you have an account) to get the download.

The specific software you want to download is called "Symantec Workspace Virtualization 6.1 MP1 HF1 (formerly SVS)".

The download includes a trial use key. However, during installation when you are prompted for the license key, you also are given the option to obtain a free license key for personal non-commercial use at the following link:
http://www.altiris.com/svs-free

(The Altiris website link still works. You don't have to enter an email address, just accept the license agreement, and the license key will download. Enter this key into the software installation instead of the trial use key.)

If you haven't used it before, the software itself is very simple to use and is compatible with both XP and Vista. I tend to use it a lot when trying out new software -- if you install something and don't like it, simply deactivate and delete the layer after installation and it is gone from your system like it was never there (if only Windows uninstall worked as efficiently...). You can also review a deactivated software layer to determine exactly what changes the software is making to your machine as well.