Since you don't tell us what engine you have, I'm going to assume its the Duratec. You really should include this information in your post if you want accurate help.
From what I can tell on the Ford Technical CDROM, the crankshaft position sensor is accessible right next to the crank pulley, which is on the passenger side of the car. You'll have to jack it up, remove the wheel and the splash guard, and the sensor will be just to the right of the pulley (you should see the wires plugged into it). According to the manual, just unplug the sensor, unbolt it, and pull it out.
Sorry if this is wrong, but I'm going by the pictures in the manual which are a little disorienting.
