I haven't done this, but I looked for a LabVIEW instrument driver for you. I couldn't find one on NI's site. Do you have a LabVIEW instrument driver or are you making direct serial calls. If you're making direct serial calls, I would suggest using NI-VISA. It's much easier to build an instrument control application with that as opposed to the straight serial calls. In addition, if you have LabVIEW 7.0, use the new Instrument I/O Assistant. It makes these applications tons easier!
J.R. Allen