DNS = Doppler Navigation System

When you first load the 707 into FSX, open the Flight Planner and you will see that there is already one loaded (KSEA - KSFF). This plan ALWAYS loads when you load the 707. Reloading the aircraft WILL reload the KSEA - KSFF flight plan and whichever other one you had will be gone. The DNS doesn't actually use the plan itself, but the plan is a MUST HAVE for the DNS to work.

My suggestion would be to pause the flight (save one included) and put everything where it needs to be for the flight to continue and load your flight plan. Once that is done, unpause FSX.

These are the main ones that you will need so your engines don't shut down:
Battery Switch ON
Bleed Air Switches ON
Manifold Valve Switches OPEN
Transfer Valve Switches OPEN (just in case you need fuel from them)

Load your flight plan. This won't be a problem if you are flying VOR to VOR. If you are flying an FS Flight Planner flight plan, you really need the default GPS 500 so you can use the menu to change the waypoint you need to head for, or it will return to the first leg of the Flight Plan, which could be a LONG way behind you.

Mark