For a Mach3 based printer like ours, you will need to be able to control 4 axes. you can do this like we are, using a very inexpensive 3 axis board, similar to THIS. We use a 3 axis version we source directly and an EasyDriver for the extruder stepper.
Once you have 4 axis control worked out, you then need a power supply. We supply an ATX PSU that has plenty of power for adding a heated bed later if you like. A decent PC power supply will work and be pretty affordable.
For temperature control of the hot-end, we use a standalone controller, like THIS. If you use that one, make sure you cahnge resistor #5 to a 15k to 20k and use a 100K thermistor. With that, you can control up to 480F and stay plus/minus6 degrees F
And last, you need motors compatible with your controller board. There's tons of stepper motors out there to choose from. You really can't go wrong with a nema 17 4-wire stepper motor. They're all made by wantai prob., so don't worry about being too picky. Get around 3800 g/cm or more, and you can print with the big guys.
Hope this helps, I'm not the best at forum based explanations. If you want, take a look at our machines on SeeMeCNC and you can see some Mach3 based machines in action. We have links to our ustream channel where we print live, and our yahoo group is full of people building them.