Not sure if you're asking how to use ActiveX in LabVIEW, or how to use this specific function. The latter I can't really help you with. Did you get documentation? Based solely on the name and the prototype it seems you pass in some sort of hardware ID and you get the drive letter. What this ID is supposed to be, I haven't a clue.
If you're asking how to use ActiveX in LabVIEW 8.2, you basically have to use Automation Open to create a reference to an ActiveX library, and then use the Property and Invoke Node functions to use the ActiveX library. There's plenty of examples that ship with LabVIEW that show you how to do this. Attached is a simple one for the library you posted and the function you provided.
