Hi,
We're going to need a little more info about your application before we can get you a compete answer.
Your 6601 is a counter/timer board that can count and measure TTL pulses.
You can get the pinout for your board from the user manual found here: http://digital.ni.com/manuals.nsf/websearch/dd0dbb6404bc139886256721007cf16d
In LabVIEW, you can find shipping examples for various counter measurements by going to Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Counter Measurments.
I would also suggest downloading and installing the latest NI-DAQ driver:
http://digital.ni.com/softlib.nsf/websearch/90B60D5899BCCCDB86256FC700581B89?opendocument&node=132050_US
-Sal