Everyone is curious exactly how they plan on desigining the game and computerandvideogames has some insight.  It looks like there will be four campaigns on the 1 gaming disk; 1 for each member.  You will need to release your star power by either hitting the proper notes on the bass or guitar, drumming the exact beat sequence, or hitting the exact notes on the microphone.  If a band member fails, there screen will likely turn gray, but the band will still rock on.  As for the singing part, there will be a tamborine like function during long guitar or drum solos to keep that person occupied.  Furthermore,

Singing is described as more in-depth, with a phoneme detector picking up “individual vowels and consonants you say. Build up enough highly judged phrases and you’ll be able to sing free-form. If you do well enough in free-form, then you’ll trigger the vocalist’s version of star power.

The game will release this fall for both the Xbox360 and PS3 and will be rated K for kick ass.