Collision Dectection in the Pose window is here to help you pose everything in your scene in an easier way ( think it's a great feature foranimators ). Imagine you want your figure to climb up some stairs : select the feet-toes and your satirs prop, turn collision detection on them and in the scene ( just below Disply Shdow button for those who don't know where it is :) and when one of the object collide with another, you can go further. Look at the image : Vic2lo foot on a prop perfectly lying on the top ! Done in about 10 seconds. I haven't tested it, but I'm sure it will work great to pose a hand holding a gun. It's usually a real nightmare to be sure fingers are ok. I personnaly think it's one of the greatest features with menus, dynamic clothing ( one of the quickest I've seen ) and raytracing ( love the SR1 transmapped hair :)