Back a few years ago, probably during the 2000 timeframe, MS had terms in their license that you could use it on multiple computers as long as you only used one at a time - so you could have it on your desktop and laptop which makes a lot of sense. I think that was a abused quite a bit. The Mac version of Office 2008 (similar to Windows 2007) provides you with 3 different license keys to do the same thing. So you can install it on the laptop, desktop, and have a backup.