Welcome to the forums.
Sounds like a very interesting project! AFAIK, there are no methods (on BlackBerry or in J2ME in general) that would do this sort of thing for you. There are implementations of Fourier transforms out there that you might be able to port over. Run it though a low bandpass filter and then detect "beats".
I was wanting to do this myself for an app that would trigger the vibrator for each beat. That would give the impression that the BlackBerry is really rocking out to a song - kind of like those cars that drive by and rattle your windows because they're cranking out the hip hop so loud.
Anyway, good luck. If you want help feel free to PM me.