I've been asked to clarify whether or not you can use copyrighted music in your Pico Day submissions...
I would say that if you have already done it and your entire movie is animated to go with a song, then there isn't much you can do at this point...
However, I STRONGLY ADVISE using music from the Audio Portal or another source that has given you permission. I really, really, really, do hate it when people use copyrighted music in their Flash and your submission will be much more favored if you make use of music from the Audio Portal or a friend or relative (or yourself). I probably should have stated this clearly from the beginning to avoid anyone from going down the wrong path, but if you still have an option, definitely avoid using copyrighted music.