Quick and Dirty Illustrator Dungeons
Well, I'm just now starting and I have a couple dungeons under my belt, but I'll be happy to explain briefly what I've managed so far. I'm using Illustrator 9.0, but I think these instructions are more or less valid in earlier versions (possibly as old as 6.0, but no guarantees).
0) Rule 0 is Learn the Basics. The Illustrator Help file can be a great resource in this regard. In particular, you need to know how to use the Shape and Selection tools, what Bezier curves are and how to create and edit them, and how to use Pathfinders and Layers. It might sound like a lot, but once you've practiced a little bit and seen how these things operate, a Q&D dungeon map should be no sweat.
Here's a Web tutorial, though I can't vouch for how easy it is to learn from:
http://thetechnozone.com/bbyc/Illustrator.htm
You might also follow some of these links to see how much information you need:
http://graphicssoft.about.com/cs/illustratortuts/
The other Rule 0 is "Save Early, Save Often." As with any computerized project, you may even want to save multiple versions so you don't do anything irrevocable.
1) Set the Grid. (Edit > Preferences > Guides & Grid) I like to have major gridlines (Gridline Every) set to my dungeon grid (.5 or .25 inches on paper). Right now I'm tracing the giant WOTC Map-a-Week with a .1 inch grid on tabloid paper (for practice), but it's a biiig map. For minor gridlines (Subdivisions) I usually choose 8; that seems like fine enough detail for major dungeon features. Illustrator saves your Grid settings with each file, so you can go back and forth. Reveal the grid. (View > Show Grid) Turn on Snap to Grid before you draw anything. (View > Snap to Grid) Later on, you can always turn off Snap to Grid if you want to do something that has to come off the grid. I also like to see the rulers, but that's just my preference. (View > Show Rulers)
2) Start with a square. Copy and paste the square (and multiples thereof) until you have your floor mapped out. This method has the advantage of providing the dungeon grid for me as I add rooms. You might as well name this layer "Floor" because you'll be adding more layers soon. I suggest making this square something other than white with a black outline; 20% grey fill with a 50% grey .5 point stroke has been working for me. It really pays to be fastidious about the floor grid. You might consider temporarily switching to fewer than 8 grid subdivisions while you're laying floor tiles, so you get maximum precision.
3) Configure irregular rooms. To get circular, hexagonal, or other strangely-shaped rooms, the first thing I do is to cover the needed area with square tiles. Then I draw the room's final shape with the Pen tool, a Shape tool, or multiple shapes amalgamated with the Unite Pathfinder. Lay the final shape over the tiles (making sure you have complete tile coverage), select the room shape and all the tiles that the outline overlaps (you don't need the room's interior), and hit the Divide Pathfinder. Ungroup that mess and delete all the extraneous elements (sometimes Illustrator adds in short line segments over the edges of the tiles; it can't be helped, but at least you end up with the proper room shape). The point of this is to preserve your grid.
4) Draw walls. You ought to do this on a new layer; call it "Walls" for now. Outline your floor for that "professional" look; I use a variety of Pen strokes and shapes (using Pathfinder for maximum speed) at 75% grey with 1 point stroke.
5) Draw features. Look to old 1st Edition products for an icon library you can duplicate, or make up your own icons for dungeon features. Either way, you must remember to get doors, statues, pools of water, and whatever else you need. Use as many layers here as you think makes sense; one for doors, one for stairs, and one for everything else... whatever. Consider making yourself an icon library and saving it off in another file for later reuse.
6) If using Photoshop to dress the thing up afterward, save a version in Photoshop 5 format, preserving layers. (File > Export...) If you've planned your layers well, then you can have the kind of fun Fast Learner is having.
Voila! With a little practice you'll be whipping out dungeons in no time. Now, about those wilderness maps....