It's been a few years since I was at Pompeii, but I took the Circumvesuvia local train line from Sorrento (where I was staying) to Pompeii for a day trip. You can also take it to Herculanaeum (Ercolano in Italian), which is every bit as cool as Pompeii. Rather than volcanic ash, it was coverd by volcanic mud which hardened into rock, preserving the site.
I took a fast train from Rome to Naples, then switched to the Circumvesuvia to get to Sorrento. I didn't want to deal with the size, noise and crowds of big city Naples...
Check out my travel web page at:
"Life is not measured in the number of breaths we take, but by the places that take our breath away..."