A little clicking around revealed some relevant information: a magazine article from 2002 detailing how to remove a stuck ignition cylinder, and a service manual describing how to get to the cylinder in the first place.
Besides this, I found page after page of people complaining about this problem in their Focus, and quite a few F-150 owners, too. The problem seems to be that the tumblers get stuck, and the key won't turn in the ignition any more.
Although I bought mine independently, there is a helpful fellow online who appears to be a good place to get ahold of a replacement. Check out http://www.focusfanatics.com/forum/showthread.php?t=121739
for more info.