I've been lurking in this thread for a while trying to come up with ideas, and now I'm getting ready to begin the build. I had a small business in High School building Adirondack chairs, they're easy enough to build, but cutting out all the pieces is really time consuming. I've wanted to experiment with building a CNC machine for years, but now I have a good excuse to make an attempt.
The machine I'm working on will (for now anyway) be a 2-axis 2D cutter using a Rotozip cutting tool to basically fulfill the role of a band saw and a drill press. I'm putting it together using a Duemilanove and the from Adafruit Stepper Motor shield. The horizontal axes will be driven by bipolar stepper motors harvested from an old DMX-controlled DJ light, while the vertical axis will most likely be controlled by a simple DC motor with limit switches since I don't need precision, it just has to be able to pull up, move, then plunge back into the wood. I might try a router bit in the tool, but since I'm only planning on cutting 1" thick wood, I see no need to go out of my way designing a vertical axis at this time.
I'll post updates as this rolls along. Here's one now because I forgot to mention it earlier. I ordered the stepper motor shield a week or so ago, but while I was waiting for it to come in the mail, I noticed that my local electronics shop had ULN2003A Darlington chips in stock. I bought a 4 pack (for $3.00USD) and started playing with one the other night to see if I could get the motor running off of the 12vdc feed from an old ATX computer power supply. I figured I'd play with this to get an idea for the coding as I waited for my motor shield. Somehow (most likely alcohol induced) I managed to insert the ULN2003A into my breadboard backwards. I wired everything up using the 4-wire schematic from the Arduino Stepper library reference page, and it didn't work. Eventually it donned on me to make sure the chip was in right, and that's when I realized that I had just sent 12vdc straight into 4 of the digital pins. I went to unplug the arduino, but I touched the ATmega328 and got a first degree burn (which was a good indication that I did something wrong). So with my arduino dead as a doornail, my motor shield arrived the next morning, and here I sit with no arduino to play with until my new one arrives within the next day or so.