You could just place your scanned drawings into a Word document and turn it into a PDF, and upload that.
But I would recommend checking out Manga Studio by the people who make Poser. It is purpose built for doing what you are talking about. I played around with it a few months back. You can download a free 30 day demo to try it out.
http://graphics.smithmicro.com/go/mangastudioYou could also try Comicbook Creator, but I don't know anything about it.
http://www.mycomicbookcreator.com/products/detail/description.html?id=32-Mark.