Here is a small VB script which will revile the original windows key entered on an installation.

It won't generate keys. It's not a keygen. It simply shows you which key your windows is running on so you can take note of it for future installations, Having lost the original documentation.  

Works with XP, Vista (all versions) and possibly 2000 and below, Not checked...

Simply double click and Bingo! Unpack from ZIP archive first, Won't run from the archive!!! Extract before use.

That's illegal Cloud. You really think that would be posted here?

I posted this because there isn't really any out there already...
All gens but nothing to tell you your original key.

I'd expect lots of people would lose their product key and have to use a generator, Even though they've paid for a key...

Also, Not all XP key gens for instance will work with all XP distributions. It's pot luck and even when you do find one for your exact build, You could try 15-20 keys before you find one which works.

Just out of curiosity.. Because it occurred to me while reading through this again. You said "Generate a key for your machine" but if your machine is currently in use, Then it must have a key already entered? If so, then the key viewer i've attached above, is exactly what you want... ?  :-/