Check the manual for the instrument. Some instruments do not have a specific command to go into local (or remote) mode. Tektronix oscilloscopes use the GTL command to Go To Local. HP and Agilent instruments do not have a command for this.
It's been a while since I used LV5.1, but in LV6, there is a VI under Instrument I/O->488->488.2 that allows you to set instruments into local mode. Hopefully, the same VIs exist in LV5.1.
Rob