Vista - Finding Software license data from an old system disk

Hi, can anyone help please. I had a power surge kill my old PC and had to buy
a new one, it has come with Windows Vista installed but all of my old
software was installed on my old IDE drive from the broken PC. I am trying to
find the License value in the Registry from the OLD disk which was running
Windows XP SP2 for my recently purchased version of Nero 7. I have tried Nero
via their website and am still waiting for anything other than an automated
response. Of course I did not print out the web page telling me this license
information when I paid for the download of Nero 7. I would have to try and
retrieve this from the old system disk which is now fitted into the new PC
(but not as the boot disc) using tools available to me under Windows Vista.
Sorry this is so long but when I tried asking Microsoft they obviously did
not understand my problem judging from their response.