pulse controlled stepper motor for tachometer

Hi
I am a total newbie but I have managed to set up and control a Swithec X25 stepper motor using a potentiometer but I am more interested in trying to read the pulses from the ignition coil and hence be more accurate since making a pulse/voltage conversion with external components and feeding that voltage to Arduino is not be best solution. And also that could also be used for showing the rpm in a LED display as well.

This a popular project and a search of this forum or the net in general turns up lots of hits.

since making a pulse/voltage conversion with external components and feeding that voltage to Arduino is not be best solution

It's pretty much the only solution.
Often an opto-isolator is used to protect the arduino from damage but there are other ways. they all involve external components.