Hoping to spark media interest in PlayMedia’s $15 million copyright infringement suit against Nullsoft, lawyers for the former said Monday that they have added MP3.com as a defendant — though the action was actually taken a month ago.

PlayMedia’s “news,” however, comes just days after MP3.com announced it was going to launch an initial public offering and expected to raise more than $115 million. Insiders noted that by naming MP3.com — which has become the boogieman of the music industry since its site allows access to artists’ music — PlayMedia gooses media interest in a case that’s become a hot topic among ‘Net denizens but has so far been largely ignored by the mainstream media.

PlayMedia claims that MP3.com has been distributing WinAmp, which contains a decoder infringing upon PlayMedia’s software (a decoder compresses audio files and allows them to be distributed on the Internet). Execs assert that MP3.com’s version of WinAmp contained a Nitrane engine allegedly developed by Nullsoft, but which was in fact based on PlayMedia’s copyrighted technology.

A federal court judge granted PlayMedia’s request for a preliminary injunction against Nullsoft on May 6. Nullsoft agreed to the injunction and has ceased distributing its MP3 decoder containing Nitrane. “If, as we alleged, the MP3 decoder in WinAmp infringed upon PlayMedia’s software, then by logical extension MP3.com owes a heavy debt to PlayMedia for our MP3 technology,” said Brian Litman, CEO of PlayMedia.

Nullsoft execs said agreeing to the injunction was “not an admission of guilt and preserves all of our defenses for the trial.”