difference between a stepper indexer and a stepper drive

[pcroxford]

Does anybody know what the difference between a stepper/indexer drive and just a plain old stepper dirve?
I have been looking at the selection of parker compumotor drives available on eBay, and by looking at the specs from Parker, I can't tell how I'd need to wire 3 of these things to my parallel or serial port. I am assming that most CAM softwares can output step/directon from the G-code. How is the data coming from 1 port on the PC distributed and divided among 3-6 axes, each with different drives? Can someone fill me in?
pleeeeeease!!!