We are going to Italy in October for 11 nights. We plan to start in Rome (2 nights), spend 7 in Tuscany and end with 2 in Florence. To get to Tuscany from Rome should we drive or take the train? We would like to spend 4 nights in the south in either Siena or Montalcino and 3 nights up North in either Lucca or Montecatini. Should be rent a car for the week from Rome or Siena, or should we take trains and buses? How much would a car cost for a week with automatic?

Take the train from Rome to Chiusi and rent a car there. The Avis office is very close to the train station. You can't take a train directly from Rome to Siena, so Chiusi is a good choice. You can see on the map that it is in southern Tuscany, an easy drive to Montepulciano, Montalcino and ultimately, Siena. This area, plus Chianti, is what everyone imagines when they think of Tuscany. Lucca and Montecatini . . . not so much. While both cities are fascinating, especially Lucca, they're not in the most scenic part of Tuscany.

If you are serious about seeing the countryside, you must rent a car. It is the only way to get out there and discover all the wonderful hill towns and wineries. You can only go to cities on the train.

How much would a car cost for a week with automatic?

You might look at the Auto Europe website. The great majority of automatics in Europe are the luxury cars - Hi $. The one exception is that some Smarts are automatics. They have small (800cc) engines. Good city cars but definitely the slow lane on the autostrada.

I lot of people take a short train ride to a town near Rome and pick up the rental car (Chiusi, Orvieto ...)

Barney18,
A car is the only wat to see some of the Val d'Orcia efficiently. Many of the hill towns have no train stations and bus connections can limit your options.
I have a big file on southern Tuscany, too big to post, if you are interested e-mail me.

Henry

I would rent a car and drive to Tuscany. It really isn't that far, maybe 175 miles (2 1/2 hours or so). I imagine a car in Italy for a week is probably about $800 right now since the dollar is so low compared to the Euro. I also would recommend autoeurope. They have the best rates.
Also, I would be sure to check out San Gimignano while your there. IMO, much nicer than Lucca.