I just tried the remote programming trick with a leftover Freestar remote we had laying around and it worked first time. For the record I have a 2004 Mountaineer Premier.

This is exactly what I did:

1) Got in, hit unlock on the door so all doors were unlocked.
2) Put the key in the ignition and waited for the seat to move into position.
3) Rotated the ignition to run and back to off 8 times ending with the key in the run position. Each turn was less than a second in between.
4) I heard the doors lock (or maybe unlock and lock I'm not sure) once the final turn was completed.
5) I hit the door lock on the spare remote within about a second or two of completing step 4.
6) i pulled the key out of the ignition.

Now the Freestar remote works with the Mountaineer. The Freestar remote has two power side door keys that obfiously don't do anything but lock, unlock and the tailgate all work the same as the original Mountaineer remote. As for spare keys there's no getting around that I'll have to visit a locksmith

 

You can visit a locksmith if you want to else you can visit dealership also.