Semi-legal Software?

Question: So, I *LEGALLY* purchased some software, but then I lost the CD registry (some stupid number on the CD case). I still have the CD, but not the stupid number required to install the program. (I bought this a while ago, but needed to reinstall). Is it illegal for me to get one of those key-generators off the internet to generate a working CD registry doohickie? When I head home from work, I'll get online and see if there is even such a thing for this old program (meaning I'll waste time on AIM and homstarrunner) Yes, I'll be on AIM. First time in months. Anywhoo....