Your not going to find it unfortunately. I looked before I started on the dj. The only decent full-screen winamp front-end I could find was at the winamp.com plugins section and it was very lacking in the features. As for vertical forget about it.
Make it. The source to the dj is mostly api calls which work in Vis C++ almost exactly the same. Just port it and combine it with the gameluancher source, or something that can support rotated text.
OR if you have a radeon card, thier newest drivers support rotating the display at the driver level. It takes about 10% of the normal framerate but for a mp3 player I don't think that would be a problem.