jillyjoey -- sorry for the delayed response!
i do have a stability ball and LOVE it -- i use the Denise Austin Shrink your Female Fat Zones workout DVD with it (and hand weights), and have recoreded some shows on FitTV that use the ball. I also purchased a book with strength training routines using the ball that i love. for me, it feels easier on my back to do these on the ball. you can also do pilates with your ball and use it to stretch. I think using the ball will strengthen your core muscles, which aids in your weight loss; but like any part of a workout routine it is all the components that bring the changes.
so examples of exercises i like on the ball are: sitting on the ball -- bicep curls, delts, shoulder presses, overhead triceps dips; back against the ball feet flat on the floor to do various crunchers; lying with my side against the ball and doing various leg lifts; lying on the floor with ball in between feet to do inner thigh and lower abs