I´ve written about virtual computers before and found a nice way program to make the same method available for virtual software installations. Altiris Software Virtualization Solution lets you install every kind of software in a protected environment that prevents access from this software to your core system. This is great if you want to try out some new alpha / beta software or software that you are suspicious about.
PcMag has a great review about the software and offers a download for it as well. Its free for personal use and can be setup with ease. What the software does is the following, it creates a layer for the software that you want to install and emulates the surrounding operating system. Everything the newly installed software does is now done inside this layer and not in your real operating system.

Software Virtualization With SafeSpace
System Virtualization With MokaFive
Spamato anti spam solution for email clients
Remote Control Software Teamviewer
Sandboxie
http://www.sandboxie.com/
does something simmilar,originally I thought it was for sandboxing IE only but it works with other software as well
SVS 2.x free for “only 120 days” :-(