You need Application Builder to create a DLL from this VI (the same version as your LV - you can create DLLs in 6.0 and 6.1 ... I'm not sure about previous versions). In case your LV package doesn't include Application Builder (it should be an entry in "Tools" menu > "Build Application or Shared Library"), contact National Instruments for purchase related information.
Another solution is to control LV as an ActiveX Server (if HPVEE has this possibility).
If you have a version of LV which cannot build DLLs, you may create an executable to do the whole "digital line reading" and save the results into a file.
Hope this helps