I'd say use the Service Control Manager APIs:
hSCM = OpenSCManager( 0, 0, GENERIC_READ );
hService = OpenService(hSCM,
"Microsoft Internet Information Server",
SERVICE_STOP|SERVICE_START );
boolResult = ControlService(hService, SERVICE_CONTROL_STOP,
&structStatus );
/* or */
boolResult = ControlService(hService, SERVICE_CONTROL_START,
&structStatus );
This is just cut'n'paste from the API docs, but should get you on your way ...