Being a true LabVIEW weenie, I'd highly recommend borrowing the LabVIEW Student Edition CD from last year's kit of parts (I think that you can also download an eval version from
www.ni.com). It's very easy to configure a serial port and generate a few bytes in a loop based on a slider.
For reference, I've attached a pair of VIs that I'd created for last year's competition to control a Mini-SSC (purchased from Jameco, provides 8 PWM outputs controlled via serial port). "Mini SSC.vi" is the "GUI" and "write to Mini SSC.vi" is the low-level "function" that writes data from a serial port.
Good Luck!