Circa 2006 I acquired a Harbor Freight Micro Mill. I spent time on and off converting this mill so that I could control it via computer using a variety of parts and kits found online. The 2 biggest parts of this was finding a set of mounting adaptors to replace the hand cranks with stepper motors and finding a stepper motor driver. This was right as the RepRap project was taking off, so options were limited on how to drive something like this. Fortunately I found a kit designed for the micro-mill class of milling machines, so I didn't have to fabricate my own mounting hardware, and HobbyCNC had a nice kit for hooking up a parallel port up to some stepper motors. Initially I ran the machine using windows based software, but when that machine physically died I switched over to a BeagleBone Black which has some nice features for this type of work. To control a stepper motor you end up toggling lines on the parallel port in a specific sequence, which if the computer gets too much too fast, i.e. an interrupt, etc... You can miss steps, causing errors in the final cuts. The BeagleBone has a couple of Programable Realtime Units (PRUs) that run alongside the processor, so they can chug along flipping bits, and not worry about anything else like networking, or mouse movements. There is even a nice Linux distribution called MachineKit for CNC control applications using the PRUs.
The first 'real' projects I did with the machine were mostly artistic: cookie molds cut out of oak, and copper gear-shaped tie-tacks for our wedding.
