I will be purchasing the XTi later this month and am trying to decide between purchasing the kit which comes with the 18-55mm or purchasing the body only and separately buying the IS version of the 18-55mm lens. Is the IS version worth the incremental cost? I am a newbie to the world of DSLR, so I don't have any other lenses. I will mainly be taking pictures of my kids playing sports and family shots. Any help is appreciated.