The Delver's Dale map is a Christopher West map, if I am not mistaken. He's a great cartographer who's completed lots of work for Wizards of the Coast. You can find his website here http://www.mapsofmastery.com/fantasy.html

If I am not mistaken, he does use Photoshop. If you already have some amount of skill in Photoshop, you will find making maps to be different, but not necessarily complicated. I am just getting started and have already done some very pleasing work. I suggest you get started with Ascension's tutorials. They are well written, easy to follow, and have good support. I started with the Atlas Style tutorial and got some amazing results on my first attempt. After you feel like you have gotten your feet wet, branch out and look at the other tutorials and styles available here. And look into non-map related tutorials. I recently picked up a book on digital painting. The techniques I discovered have helped me make some very nice textures.

It does take a little bit of time investment, but start with the program you know the best. Photoshop is very powerful and well supported. Many of the GIMP tutorials are easily translated to Photoshop if you know PS well and can translate the differences in nomenclature. Using Ascension's tutorials, I pumped out my first map in just under three hours and it was loads of fun.