I have to admit I have not done any extensive testing, but this little tool seems like a good thing to have around!  For more information, have a look at Sandboxie.

About Sandboxie

When you run a program on your computer, data flows from the hard disk to the program via read operations. The data is then processed and displayed, and finally flows back from the progam to the hard disk via write operations.

For example, if you run the Freecell program to play a game, it starts by reading the previously recorded statistics, displaying and altering them as you play the game, and finally writing them back to disk for future reference.

Sandboxie changes the rules such that write operations do not make it back to your hard disk.

ttfn

David