.Servo or stepper I don't think there is any difference to Mach 3/4... it's a pulsetrane with a direction signal.
Think you'll feel limited in the end with a parallel port (and mach3 as its not been developed for years, and there is no intention to update it either). Mach4 is probably fine for a simple mill at present, but I'm not sure how many people have converted fully from mach3 to mach4 in a production (receiving payment for goods produced) capacity at present... its sort of in a long term development phase (more for the other bits of cnc at present than mill though (lathe, plasma, etc). That being said, and I do have a licence for it, it is very fast and smoother in motion than m3, and will be great in the end.
Rob