If you never want the printer to start printong from another tray when the
correct tray is empty.
Open Printer Preferances, select the Paper/Quality tab, select the paper size
that applies, select the tray in Source. It is probablty set to Automatically
Select at the moment, right?
The instructions apply to the PCL6 driver for Windows XP but there should be
similar options in other drivers.
Tony
MS MVP Printing/Imaging