If you didn't know this, any single license of Microsoft Office is eligible for installation on two computers. Neowin.net has people who read the fine print, that is the boring 'Terms and Conditions' of MS Office. Careful reading shows that you can install a single copy legally on two devices.
Microsoft calls one computer the primary computer. That may be your desktop (if it's a laptop, that's fine too). The second computer you can install it on is your portable computer. This is the laptop or tablet that you carry around with you.
So from now on, be sure to read the license agreement. You may find some unexpected discounts, privileges or refunds hidden in there.
Oh, and another little thing. Microsoft Office Home and Student 2010 can be installed on three PCs.