read performance ford. one of the writers has an st170 turbo. It is possible.
The only difficulty is the management of it all. You can't use the focus ECU as its not ready for turbo charging. I don't think it has the capability to monitor the Manifold pressure and other sensors need for turbo charging. The options are aftermarket ECUs like autronic or motec etc, or you could find a turbo charged car and use the ECU from that car as long as you've got the software.
Have a word to another tuner. Pumaspeed aren't the be all and end all so to speak.