Hi,
You can use the NI-DAQ driver to control your 6024E card. I would suggest programming it in LabVIEW, but you can also program it in C using the documented C functions.
You can download the NI-DAQ driver here:
http://digital.ni.com/softlib.nsf/websearch/BEC182021CEB566C86256EEE00696562?opendocument&node=132060_US
-Sal