I've gone twice the way Rick Steves says to do it. In Rome, you transfer to regional type of train that takes you to Naples, then you transfer to a local train that takes you to Pompeii.

The bus is called the Sita: http://www.campaniatrasporti.it/sita/5021.htm gives you a schedule for the bus from Naples to Pompeii

The local train times can be obtained through this site: http://www.fs-on-line.com/home/en/index.html just enter Roma and Pompeii. You should be given several times. As best I remember, the Eurail pass does not cover the trains from Roma to Naples and Naples to Pompeii. Might have been a discount, but I doubt it.

I never have taken the bus to Pompeii, but did use the Sita bus to go down the Amafii coast line, which I highly recommend. I don't know what it is like next month, but in the summer it is great.

Wil Orlando, FL