My husband and I just returned from our first cruise - Royal Caribbean, Voyageur of the Seas, from October 7 to 14. We made great use of the info on the site about how to get to the train stations in each Western Mediterranean port and wanted to add a bit of info on this stop.
After disembarking at the port in Naples, we were advised at the port tourist information booth that the newspaper stand across the street sold tickets for the bus/train. At the newspaper stand we were able to buy a ticket that provided access to both the Naples bus/tram as well as return trip to Pompeii for 4.5 Euros. All we had to do was take the #1 tram from the stop right there to the train station. The traffic in Naples is insane!
Also, at Pompeii, we discovered that once you buy your ticket to Pompeii, if you go to the information desk in Pompeii, they provide you with a FREE map and guide book describing all of the highlights of the site. This beats the 8 Euros we paid for the guidebook (not the greatest quality) that we bought outside the main Pompeii entrance.
I hope this is helpful - we enjoyed our trip and REALLY appreciated this web site.