To do a dumbell pullover you lay down on a bench making a t with your body and the bench. Resting just your upper back on the bench. With a dumbell above your head you lower it as low to the ground as possible then back up to just above your head. I have to disagree with trendkill though, as far as I know knowthing can expand your ribcage. This is an old school wives tale. Arnold says this is possible in all of his books, but science and kinesiology disagree. But they do work your lats and probably your chest and tris fairly well.