If you use the example that ships with LabVIEW 6.1, titled "Finite Pulse Train (DAQ-STC)," one train of a specified number of pulses will be generated and then the VI will quit. If you are importing this example VI into your own custom program, you need to ensure that it is not called from within a while loop. Perhaps that is why you are seeing the pulse train repeating itself.
This example can also be found by clicking on the following link:
http://eagle.ni.com/stage/we/niepd_web_display.DISPLAY_EPD4?p_guid=B45EACE3E6CD56A4E034080020E74861&p_node=DZ52328&p_submitted=N&p_rank=&p_answer=&p_source=Internal
Regards,
Justin Britten
Applications Engineer
National Instruments