The standard installation of NI-DAQmx puts an item into the Start menu: Start->National Instruments->NI-DAQ->NI-DAQmx C Reference Help.
Look under C Functions->Channel Configuration/Creation->Create Digital Output Channels, and Write Functions, various DAQmxWriteDigital... functions.
Look in the NI-DAQmx Concepts section for various kinds of information about digital output.
Look for the C-language examples under Program Files\National Instruments\NI-DAQ\Examples\DAQmx ANSI C\.
John Weeks
WaveMetrics, Inc.
Phone (503) 620-3001
Fax (503) 620-6754
www.wavemetrics.com