I am surprised Lincoln didn't respond, he is generally a responsive fellow. I would first suggest emailing him again, and getting his input. Otherwise, I would ask on modules@perl.org what they think about the namespace to use. If much of the MP3::Napster code has been left alone, a good place may be MP3::Napster::Opennap. Personally, I would suggest doing what you can to leave MP3::Napster alone, and simply subclass it with MP3::Napster::Opennap, overriding method names if you need to.

Cheers,
KM