DC,
The best board to accomplish your task would be to use a counter board 6602 or a counter on one of the E-series DAQ board (if you have one already).
The counter can be set up to take a variety of measurements based on TTL signals (0-5V digital signals). The DAQ driver ships with examples of how to do event counting written in LabVIEW, C, Visual Basic.
Let us know if we can assist you further.