so i have one at home, blew it up once, rolled around the floor with my little sister then deflated it..

so Im ready to take it back out and use it for its real purpose! this may be a silly question but those ball exercises would build muscle correct?

It depends how you use the ball

Here are some beginning ball exercises:
http://exercise.about.com/library/blbeginnerball.htm

Yep, I love my ball! Love it! I took a ball class once and learned so much. One of my favorite things to do is to use it as a weight bench. You can lie with your head/neck on the ball and hold yourself up, lifting your pelvis into the air. Hold your pelvis in the air while working the arms with weights. It will work the hips, thighs and rear at the same time. You can also put a weight on your pelvis and do pelvic lifts lowering your bottom to the floor and then raising your pelvis toward the ceiling.

There are so many thing to do with the ball. I'm on the lookout for a good routine myself.