automatic setting of system time

On operating systems such as VMS and RSX it was possible for a program to receive a time signal via an RS232 port and tehn to update the system time automatically. I wish to do the same on Windows NT from a Labview application. Reading the time signal presents no problem, nor does comparing the time read with the system time.
I am aware that some programs are available that use a time signal from teh net to set teh system time but that unfortuenately is not an option. Can anyone supply teh missing information to enable me to code a module for setting the system time without operator action. If so please mail me David@alpha-comp.co.uk