dardm80,
What an interesting application.
How you control the flow meter will depend highly upon the interface between the PC and the instrument. If you are connecting through GPIB or serial, an instrument driver may exist. Just search www.ni.com/idnet for your flow meter. Alternatively, you could use calls to your instrument through VISA writes and reads. There are a few examples within LabVIEW that demonstrate VISA calls. The exact syntax will be instrument specific so you will need to consult the instrument's user manual.
If you are connecting through a data acquistion board, then you will use NI-DAQ VIs in LabVIEW. Again, there are many examples of DAQ input within LabVIEW.
Good luck!