Hi Jason,
If the pulses come from the coil you can calculate the frequency coresponding to any particular number of RPM. For a 4 cylinder 4 stroke engine there will be 2 pulses per revolution. So for example 1500 RPM would be 3000 pulses per minute which is 50 HZ. (3000 /60 = 50 HZ ) You would just need a resistor and a 4.7 volt zener diode to clip the signal from the coil primary do a level that could be fed into a PIC or a frequency to voltage converter. If you want some code to get you started writing the code
there is some here on my website. It includes the source code. This code is more complex than that needed for a car rev counter as it was designed to give accurate readings down to a low speed (60 RPM) It also includes code to alow it to be used with sensors the give between 1 and 99 pulses per rev.
Les