Sandboxie is an interesting software which allows you to run almost all the program which runs on windows in a sandbox i.e An environment which does not get reflected in your actually system and see how it performs.

This could be a good alternative when you try new programs and you want to see how it works first and impacts your system performance before it actually starts making changes to your system.

This could also be useful to aovid some percentage of malware or spy ware activities. Run the newly installed program in it and if you find something  unusual just get rid of it. As the changes made is still not into your hard disk but still kept on sandbox you are safe.

I can probrably spend a complete day telling about this application but its not really required. They have a great FAQ page which is more then enough to fulfill all you wanted to ask. Try Sandboxie and tell us your experience.