Since there is now four components (mic, drums, guitar, and bass) the screen has to be divided up. The words are up top for the singer to read from with some handy visual keys to tell you what key to sing in and how long to hold a note.
The standard guitar is on the left, Guitar Hero style, with the bassist all the way on the right.
The drummer gets placed right in the middle of the people rocking out the guitars, just as he/she would on a real stage. In case your wondering, the orange line in the drums section is for the foot pedal.
Harmonix has yet to say if when you're playing online with friends if you will only see your particular music note section or if you'll still see all four. All I gotta say is, I can't wait for some four player co-op Rock Band (and maybe in that other game too...)