I'm so excited to start! I'm so pumped!! Been reading and watching the infomercials and i'm just ready to go.

One question

1. regarding pull up bar replacement. Would it be alright if I did a workout similar to the pull up? Could I use an exercise ball to lay my belly on and lift weights from my sides to work my back? Almost like a reverse fly. This seems it would be harder than using the Bands.

My opinion... Bands or bar, your choice. But I would not do any other substitutions.

My opinion.

I agree with Iskarp,

the thing is that you would normally work the band to failure.
using the exercise ball would not give a full back target.

The thing about doing reverse flies is that it would be almost equivalent to doing rowboats off a machine. Pull ups work a wider range of the back, so you'd be doing a completely different workout than the one instructed in the video.

I get your reasoning behind changing the exercise, but the idea behind the program is resistance training, using your own body weight against you. When you do pull ups, the resistance of using your body frame is more weight than you would be able to lift in dumbells laying on a plastic ball (I've seen a couple of nasty injuries with people using heavy weights when the ball bursts.
The second issue is that the movement of a reverse fly is at a completely different angle than you would be when doing pullups, and working completely different muscle groups. The back fly is a single muscle exercise, while a pull up is using traps, triceps, shoulders, forearms, lats, Teres (major and minor), and Rhombodeius. You will get far more out of the bands or bar than you ever will doing a fly.

Yeah, i figured it might *POP* Instead i used the resistance bands and it worked pretty well. I'm so sore! My back has never been this sore. I think i might just stick with using resistance bands for now and maybe get some heavier ones this week.

*sidenote* i was SO pumped to do the next p90x workout that i actually watched the program last night before i went to bed THAT GOT ME EVEN MORE PUMPED!