Just install it yourself. What's the big deal? And, where you don't have the original disks, toss the installers you downloaded on the HD in a folder called "installers." That way, if they ever need to re-install for some reason... they're good.
Your MS Word installer is part of a larger Office package, right? That's pretty expensive software, so are you sure the copy you're giving away with your computer is legit, or are you no longer going to be using it yourself? It would be a nice perk for a buyer, but just don't pirate crappy software, even from Microshaft. 😉
You could always install a copy of NeoOffice, which is completely free, and works really well. They'd probably appreciate that about as much. At least I would. 🙂