Thanks Aleksandar.
I have read through he links you suggested, but these do not help to meet our basic requirements. We do not wish to make use of forecasts, and we also don't want to create production or purchase orders directly from sales orders, which seems to be the main function of the order planning window.
If NAV is truly incapable of planning forwards (how can this system be called 'MRP'?) are there any third party MRP tools available which can work with NAV?
Mark