Does anybody know of any good how-to books regarding fundamentals of cartoon illustration?

I do most of my work in pencil. I am trying to make the move to digital illustration, but I am having trouble figuring out how to make my digital work look like my pencil work. Right now I have Photoshop Elements as well as GIMP.

My problems aren't so much to do with the interfaces of the programs, but more with how to emulate my pencil sketches when I am drawing digitally. Is it just me, or is digital simply unable to capture the nuances that you get when you draw in pencil? Whenever I try, things just look bumpy, lines too hard, etc. I suppose I could go in there and manipulate shit pixel by pixel, but that seems like it would take days to get even the most simple project done.

Does anybody know of any good websites or instruction books out there for people just beginning with digital illustration?

Thanks!