If you have an OEM version of Office, then you are not allowed to install it
on a different computer than the one it came with.
If you have a retail version of Office, and if you have the original CD and
product key, then you can uninstall from the first computer by clicking on
Start | Control Panel | Add/Remove Programs | Microsoft Office | Remove. You
can install on the second computer by inserting the original Office CD and
following the instructions on your screen from the setup program (which
should start automatically). If you have problems activating the second
installation online, use the telephone activation method.