The rail service in Italy is good, the trains are generally on time, clean and the tickets are not expensive, you can always use Credit Cards for payment.
From wherever you are making your journey within Italy the Italian State Railways have an excellent web site that allows you to search timetables (versions in English and German)
When travelling to large cities such as Rome for two or three nights I highly recommend you use the train, First class is not that much more and is extremely comfortable.

For motorail
A good site for motorail service in Europe is
www.railchoice.co.uk
For the Italian State Railway, including international trains to and from Italy.
www.trenitalia.it

For an excellent website that provides information about travelling to Italy by train visit Seat61, this website provides information about fares and timetables based on travel from the UK