Welcome to the Guild Dannyl, I can certainly identify with your desire to be free of the Wizbro treadmill of rules editions (I myself couldn't make the leap from 3.5e to 4e). There is also something to be said for wishing to create your own material, though this is a very time consuming venture. You've come to the right place to learn how to do digital mapping. I'd also recommend checking out the Obsidian Portal (if you haven't already), which is a free wiki based site that allows you to create your own campaign/campaign setting related site to store all of your information. At any rate, look forward to seeing your maps (check out the tutorials page, there are tons of Photoshop related walk-through's there).

Cheers,
-Arsheesh