Quote Originally Posted by Dark Sage View Post
False Swiped. (Although, I believe that you fight him at a point where you do not have access to that move anyway.)
You haven't done what most Pokemon players do in Diamond/Pearl - visit the Veilstone mall. False Swipe(TM52) is a buyable TM in the Veilstone Mall, which is obviously accessible long before you face Giratina.

And yes, I always save my game before trying to capture a legendary. Usually because I want to see if I can get good IVs for it.