>Lauren, You'll find that shoulders and arms are similar to
>Cathe weight work for upper body.
I find Shoulders and Arms very different from Cathe: some different moves but, more importantly, a different sequencing of moves (circuit rather than straight set) that is much more effective.
S&A is my favorite P90X workout!
As for which one to do: S&H may be more familiar (because it's a weight workout), and might be a friendlier intro to P90X. On the other hand, if you feel ready for a challenge, Core Synergistics is a very different kind of workout that really hits the core. It is both a core workout, and a functional fitness weight workout.
Either way, you can't miss!