It's supposed to come out in 2007 as a direct-to-dvd.
http://www.youtube.com/watch?v=6_p8lFxMQTM
Here is a summary of what Wikipedia has to say:
- Melody isn't in it (It was confirmed by Tara Strong (who voice her) on her myspace)
- Since Melody isn't in, it is likely that this will be a prequel.
- Another reason it is probably a prequel is because a short musical number from the film was released on The Little Mermaid Special Edition DVD (
http://www.youtube.com/watch?v=y7IRlcLp624) and from the dialouge and looks of the characters, it might be one.