Someone asked me recently what to do if you have a copy of Office installed on an old, ready-to-be-decommissioned computer and want to move the software to your new box. Problem: you have lost the installation product key.
Interesting question. This has never really been an issue for me at work because we have a volume license (and therefore, all copies use the same key), but I could see how this could be a problem for a home user. So, I did a little research...
Let me start out by saying that if you own an "OEM" copy of Office (one that came with your computer), the license is tied to the hardware - you cannot install it on another machine. But, if you bought a boxed copy of Office, you are entitled to install it on another machine, provided you remove it from the old one.
OK, so we're established that you're allowed to move the license to a new box. Now what? We've lost the product key and won't be able to install it. You have two avenues from this point:
1) Contact MS and ask them for a new product key
2) Use a software package to retrieve the original product key from your old computer
The former case is pretty self-explanatory. For the latter case, you could check out Magical Jelly Bean (yes, it's really called that). MJB is an open-source package that will retrieve your original key for you.
Note: I assume that using such software does not violate any software laws, but I have no idea as to the degree of legality of this program. Just a friendly disclaimer... :)
Anyway, hope you find this info useful.
P.S. Thanks to the other Chris for telling me about MJB.