|Read the license agreement you OK'd when you installed it, I am pretty sure that you are not allowed to reinstall it on a different system.|
If you install it without activating it, it is a trial version and I believe it will work for something like 30 days and bug you periodically to activate it.
You can download and install free of any charge Openoffice.org for any system (Windows, Mac, and Linux). It can open MS Office formats as well as many others. You can set it to save in MS Office formats by default so everything is more portable.
You have to be a little bit crazy to keep you from going insane.