Ankesh,
I've used the ball, the secret is the size...try the biggest one you can find...but I'm up a lot...don't do LOOOOONG stretches on the computer anymore...but using the ball has eliminated most back ache and leg ache.
Also, dropping the keyboard a little lower has helped too...but you get used to a ball very quickly...
Also try the Alexander Technique...not mine, but one that I've found really helps.
http://www.alexandertechnique.com/
Be careful at first, I forgot a couple times I was on it and ended up on my
floor, just rolled off the thing.
Gordon (One the BALL {sometimes}) Alexander