[This followup was posted to alt.autos.ford and a copy was sent to the
cited author.]

 The car has PATS (Passive Anti Theft System.) There is a tiny chip in
the key that the computer must know about before it will let the car be
started. You normally cannot use an unchipped key.

 With only one key, additional keys can only be added by connecting the
security system through the computer, since you have a 2000 vehicle (pre-
1998 can do it without that). Once you have two keys learned, you can add
more yourself without hooking up to the computer.

 If you want, you can have security disabled in the computer. That will
let any key start the car, encoded or not.

 There are some placed that sell chipped keys, but again, with only one
key, you need a programming tool to add it.

Ummm this is why car-jacking have gone way up.

I was in a locksmith shop the other day and surprised that he advertised
making security keys... check in the yellow pages

If one has TWO keys it is a simple, no cost, process to encode an
additional key other than the price of a key
containing the chip, which is around $25.   For security reasons
the same procedure sill NOT work if one has only ONE key. If the
procedure worked with ONE key, any parking lot attendant could
duplicate your key, just like they can if you give them your
house key.  You need to take the vehicle to a dealership so a
technician can download the proper code from the vehicle in order
to then make a duplicate.  You must pay for his time, as well as
the cost of the new key.

mike hunt