If you still have the key that came with the installation media find someone who will lend you some installation discs (it may need to be the same package version) and you'll be able to install it on your lappie.
If you don't have the key, Belarc advisor will be able to extract it for you. See
here for a link to this rather handy little application.
One final point. Take a look at the licence for your Office installation - many versions allow you to install two copies (desktop and laptop I think are specifically mentioned) provided you don't use both at the same time.