remsor,
I don't know what a Grable printing is, but the best way to print bar codes in that printer is by using its built-in barcode capability. You would have to consult the manual (the one that came with the printer) on what control-characters to send when printing specific types of barcode. Normally, you would have to setup your printer to use the Generic Text printer driver for it to recognize the control characters you send to it.
If you want to have your barcode label designed using the VFP label form, you would need special or specific printer driver which normally lets you control how the printer prints individual lines of a specific barcode (this requires precision layouting).
Medic