just my opinion: calculating calories and over planning the training routines is the biggest mistake for a beginner (since one is skinny he is a beginer no matter how much time he spent on the gym). Also smoking has to little to do with this in my opinion. I am not skinny (in fact just oposite) but I trained with skinny guys and saw excellent results on them. Everything can be achieved but you must forget about rules... or at least build your own rules.
When one starts training he must concentrate on his body, on every muscle he trains and not on the training routine (how many and what exercises , how many repetitions).
An example about diets: everybody is scared of eating fat food, well some weightlifters only eat fat food and guess what: they are champions, the health is perfect and yes they are not fat...
Ok... I can talk about this all day long I guess but I don't really think you want that
so I get back to my work ... good luck to you all...