Which Opto22 unit are you trying to interface with? There are several options for communicating with the Ultimate I/O brains, any of which will work with LabVIEW 6 (I personally have written drivers which utilize 2 different methods).
Depending on which unit you're talking to, you have several options for controlling the Opto unit. Many of their newer brains have ethernet interfaces as well as the more standard serial interfaces. Personally, I generally prefer the ethernet interfaces to the serial (which are the ones used in the driver you posted).