We've taken the train from Roma to Firenze numerous times. In fact, we'll be taking that train tomorrow! There's a bit of info regarding accessibility on the Rail Europe web site: http://raileurope.com/us/faq/trains.htm#handicapped

Getting around the streets of Rome with a wheelchair can be very challenging. If we knew how long you are staying and the sights you expect to see, we might be able to make some suggestions regarding the most suitable area.

Ciao, Don and Linda