I am pretty sure I have used Mp3's in my DVDs before, but this time it is asking me to register it online. Is this free? It is attempting to connect to the internet and register it, but I haven't pressed retry yet because I wasn't sure.
Yes, registering is free, provided you own a legal copy of the software. You can register it online from the computer you are using, or from a different one.
I had a problem with registering for MP3 using DVD Architect. This was after upgrading to 3.0c, after I had to reinstall all my software.
It crashed and the error was in mp3rw.dll
If you upgrade to 3.0c and you cannot use MP3 files in DVD Architect, then you should copy the old mp3rw.dll file to the installation. I found mine in the Sony Setup\DVD Architect 3.0 folder, in a zip file called mp3plugi.cab dated 15/09/2005.