And if you ARE using gimp, but have no idea as to how to go about using it for mapping, I cannot recommend RobA's Regional Map tut enough as a stating point. There are sooooo many ppl who have starting by using that tut who are now producing AMAZING maps, that I am sure that you will be well on you way. Check the other tuts out as well, 'cause you never know what technique will jump out and grab ya.

Once you start on a map, put up a WIP thread to show your progress and to recieve very helpful comments and critiques. Trust me, do not be shy to ask about any difficulties or questions you may have on your project. We are a friendly bunch here and try our best to make you a great (if not awesome) mapper. Just remember that it is YOUR map, so use the suggestions that will come and see what suits Your vision of it. We all started somewhere and it usually was not at the top of the game so don't be shy about posting your work as it progresses.

And all that was a long winded way of saying "Welcome to the Guild, the Mappiest place on the web"