If you downloaded Agilent 816x VXI Plug&Play Driver, you can use it in CVI immediately. You don't need conver anything for CVI. fp file is part of CVI driver.
In project window select menu item Instrument>>Load. Load the hp816x.fp. Add #include to your C code and you can use all function from driver.
Help about converting fp for labview describes how easy create LabVIEW driver. This convertion make llb file with VIs for every function from Fp panel. These VIs call functions from hp861x_32.dll. If you are using CVI you don't need do it. This help is only for LabVIEW users.
Zdenek