You'll need the original CD to install Word. When your cousin installed it onto your dad's computer, the installer puts all of the parts of the the program in all the different places on the hard drive where it's needed (i.e. the system folder, libraries, extension folder, etc.). The only way that you'd be able to install from the pen drive is by copying the original installation CD to the pen drive itself. I'm not even sure if the MicroSoft software will let you do that. They build all kinds of copy-proofing into their stuff to prevent that sort of thing.
