Catso, I couldn't have put it better myself!! However, that does not address gbuss' immediate need!!!!!!
I remember a skinny bloke at work (I work in a leisure club - the guy in question was not a gym instructor) conferred with one of the instructors as to this same problem. The solution was to drink those whey protein drinks between meals, adding a selection of bananas and other fruits and blending it all together. It worked, he gained about half a stone, however, it was a difficult regime to keep up and the moment he stopped, the weight dropped off!! Sorry!