There is no "let it program itself".
If you have an early enough 98 you can add a key with one already functioning key.
If it is a later 98 or newer you will need to have someone program the car to accept the new key using a WDS or NGS. There are some locksmiths as well as independent shops that can do this, but they are few and far between. Most likely you will need to take it to a dealer and pay for the service.
I would highly recomend that you add enough keys to end up with at least three so that if you loose one in the future you can replace it without going to the dealer. Adding a third key is something I did imediately when I bought both the Contour and the Escape.