I believe the parties have their own rules about what the majority/minority leader can do. A number of posters mentioned LBJ as an effective (if reprehensible) Senate majority leader, and I am quite sure it was not his personal charm and magnetism that kept his guys in line. I suspect Republican rules allow for less "tyranny" (which we could use a bit of!).
I'm more worried about what Frist should or should NOT do rather than what he can do. Technically he wouldn't need all 7 RINOs' votes but it would be better to have a voting cushion.