Taking the train from Roma terminal to Sorrento

As far as I know, you can take the Leonardo Express to Roma Termini (35 minutes, departs every 30 minutes), then take the fast train to Napoli Centrale (1 hour 15 minutes), then go downstairs to the Circumvesuviana station for the train to Sorrento (last stop, a little more than an hour, departs every 30 or 40 minutes). Three trains, three tickets. Validate the LE and Circumvesuviana tickets before boarding, the train to Napoli Centrale should come with a seat reservation and doesn't need to be validated. (Tickets that do need validation say "convalidare" at the top.)

Zoe is correct except that your message indicates that you will be departing from either Roma-Termini or Roma-Tiburtina. From these train stations, ignore the instructions for the Leonardo Express from the airport and the remainder of Zoe's instructions are spot on. You will be on two different trains on two different train systems. About 2.5hrs-3.0hrs. to get to Sorrento from Rome. Or, there is the Marozzi bus that departs once a day at 15:00 from the bus area across from the Roma-Tiburtina train station that goes to Sorrento. No trains. About 4.0hrs for the ride.

You can also take a Train from Rome to Napoli and then a ferry to Sorrento. This is what we did and I'll do the same next time we go to Sorrento. Take a cab (agree on the fare before you hop in) from the station to the ferry pier (about a 10-15 min ride) . Not sure if Rick Steves book have information on the ferry but you can research it. I can look for info if you can't locate this.

Also check http://trenitalia.com. If you have fairly firm schedules you can book the train in advance and save yourself some money. Make sure you take the high speed trains (see Le Frecce) on their site. Avoid Intercity Trains for these are prone to delays and breakage. On the way to Napoli our train broke down and all the passengers (including us) were lugging bags across the train tracks. I can say it was in line with the "backdoor" philosophy and it was a great story to tell but if you are tight on time get the other trains.

Let me know if you need more info. Been there only once but loved the place. Stayed in a very neat BB in the middle of town that I can research the name if you want it (this was about 5 years ago)... Good luck.

Thanks for the correction, Larry, I skipped over the part about staying in Rome for two days.