To be sure, you should:
* Consult your owner's manual: This will have diagrams showing the sensor location.
* Use a repair manual specific to your Mustang's engine: These manuals provide detailed diagrams and instructions.
* Search online for a diagram specific to your engine: Searching "2001 Ford Mustang [3.8L or 4.6L] camshaft position sensor location" will likely yield images.
Without knowing the exact engine, a more precise location cannot be given. The sensor is usually mounted fairly close to the camshaft sprocket or gear, but not directly on it. It's usually a small sensor with a single or two-wire connector.