It sounds like you are using the .NET assembly for DAQmx. If this is the case it may be more straightforward to use the WriteMultiSamplePort method of the DigitalMultichannelWriter class as opposed to the WriteWaveform method. This method uses the more basic data types. There are several different prototypes of the WriteMultiSamplePort method including a two dimensional array of unsigned 16 bit integers that represent the states of the various lines on the board. For more information on these methods I would highly recommend taking a look a the NI-DAQmx .NET Framework 1.1 Help. You can find this by clicking Start>>All Programs>>National Instruments>>NI-DAQ>>NI-DAQmx .NET Framework 1.1 Help.
Regards,
Neil S.
Applications Engineer
National Instruments