I'm assuming you mean pulses of voltage.
The easy but more costly way to do this would be with a premade computer occiliscope, or maybe just a frequency monitor device, if you go that route there are many of them in different grades, with different features.
The cheaper, but maybe far more troublesome depending on your expierence route, is to use a programmable microcontroller, program it to record the pulse rate, and set up an interface with the pc via serial or usb port. I or someone else here can expand on these methods more, but we'd need to know a bit more about your project, skills, and budget.