You can use any program you want, the thing is know your tools develop a workflow that works for you, and mainly above all LEARN Program and what it can really do which unless you sit down and follow the manual step by step its gonna take some time. Best bet if you want to make maps like the featured ones, is start studying iconography, calligraphy, perspective, landscapes and architecture. DOODLE a lot, and start trying to figure out the best way to make representation of things. The best thing to do is just jump in head first start leaning what ever system you feel comfortable with, it can be photoshop, gimp, pen and paper, or even like that one guy did for the monthly challange this month and physically make some objects. Everything you do will help you get closer to your goal, and will change your though process tword completing something to the level you expect.

The simple answer, any method will do... but to make professional artist type maps, you need to have a stoke of genius or yourself become an professional artist (which takes a lot of personal dedication and people will think your "wasting" a bunch of time) in order to make something that you would consider adequate. At that point the tools become less and less and issue.