Yes you will be asked for the a software registration key. It's actually two separate keys.
Those who purchase the software online, getting the download version, the software keys are e-mailed. Sometimes these show up in the Junk Folder for e-mail, for some odd reason.
Those who get the CD version will have the software keys on either the CD or the box. I'm not sure as I get the download version.
Do not discard the software keys. If you have the need to reinstall the software, or you download the most recent version from the Butel website, you'll be prompted to register the software for it to function properly.
If you still have the original CD and the software keys, you should be good to go. Butel provides lifetime updates, so once you've bought the software, you can keep it up to date.
However, given the age of the 396T, it's unlikely Butel will update the software.