... at the Varco Immacolatella, in the port at Naples, from
where they've been leaving since autumn 2010.

Many run only on weekdays (Mon to Sat here), including those that go to
Amalfi, and the service to Pompei

As of Feb 2012, for current SITA timetables see:
__ http://www.sitasudtrasporti.it/

... with - for example - the one for the route between Naples and
Pompei on:

_ http://www.sitasudtrasporti.it/public/tpl/campania/5001.pdf

Thanks to the slow-moving traffic, there's one on whose signboard
you can read that it's going to Pompei, and another to Salerno..

The red brick building at the right houses at ticket office, see
also _ http://www.pbase.com/isolaverde/image/122851273