If you are looking to import a scan or something into a program like GIMP, I would suggest looking at Giddie's Handdrawn Map Tutorial in which he starts it off by using an already created map, if that's the style you are going for anyways. It's pretty impressive and he uses some shortcuts to make the process go a little faster. If that's not the style you want, there is a whole tutorial section and even an How Do I? forum where you can ask questions as to how certain effects are achieved.

You are stepping in to a fantasic community and I am sure you'll have no trouble finding someone to answer your software specific problems. (I forgot to mention that there's a forum section for that as well)

Welcome to the Guild, Sir.