OS X reinstallation and Amazon software. I just purchased a second hand, 2-Week old MacBook Air. I downloaded the Mac Office from Amazon. When installing, I'm prompted to enter an Administrator Password, which I still don't have, as the guy who sold me the computer has not yet given it to me.

So, can I reinstall the computer without this password? And if so, will I be able to re-download the Office file from Amazon Software Library? And, would this reinstallation solve my problem of not having the computer's Administrator Password?
I the first place, there are ways of resetting the Administrator's Password. 

Answering your questions, yes, you can reinstall the computer without this password. Just follow Apple's instructions. 

And, yes, you'll be able to re-download the software from Amazon, as stated in its Help Page:


  You can download an unlimited number of times for personal use. To re-download, go to Your Games and Software Library through the "Your Digital Items" link at the top of the screen and click the download button.


And, again, yes, making a clean installation will make a new Administrator user, with a new password which will be chosen by you.

Note: Both of the links regarding OS X reference Lion, as you never stated which version of OS X you are using. These instructions, though, will work for Mountain Lion too.