If the description on train travel is the one at the top of Europe Port Chat, I know it well. I wrote it. Read it again then just follow the instructions backwards. You want to go to Roma Termini. If you want to go to FCO International, take the Leonardo Express from Termini. All in all, you will save enough compared to the ships transportation to have a very nice meal or two.
Italian is not required to make the trip. The people that work in the station know enough English to be able to help you out.
Enjoy your cruise.
Radiance of the Seas - Nov 2006
Legend of the Seas - Jun 2007
Costa Fortuna - Mar 2008
Legend of the Seas - Oct 2008
Celebrity Constellation - July 2009
MSC Orchestra - Jan 2009
Navigator of the Seas - March 2009
MSC Poesia - November 2009
Jewel of the Seas - June 2010