I have the Rick Steves' Paris guide and it suggested to go through TGV to book trains for the best rate from Paris to Rome. But, we are going from Rome to Paris. It was not clear on the TGV website if I would be able to obtain an e-ticket (in fact, it looked as if I could not). Can I? It is enough savings (we are on a tight budget) for me to pursue every option. The other thing I thought about is having the tickets sent to our hotel in Rome. What experience have others had?
What Steves said/meant is that you get the best price going through the local train system rather than using something like RailEurope, etc. So if going from Paris to Rome you book through the French rail system. If going from Rome to Paris you use Trenitalian or the Italian rail system. However, Trenitalian generally has been unfriendly towards Am credit cards. But it a try. Recent reports have had some people being sucessful with Am credit cards. You can also use Bahn.de for scheduling information but not purchase.
Take a look at seat61.com that explains how to use the local train systems, including the French train system in their language. This let's you get the best fares. According to the site "www.voyages-sncf.com & www.tgv-europe.com can sell train tickets including the necessary seat, couchette or sleeper reservations for almost any journey within France and for direct international journeys to or from France, for example, Paris to or from London, Barcelona, Madrid, Switzerland, Rome, Florence, Venice, Milan, Munich, Amsterdam, Brussels. All the cheap deals are shown, and there are no booking fees or postage to pay. That makes these sites very useful for any European train traveller or visitor to Europe" You have to be careful to read that site and follow the instructions so you don't get punted to the raileurope site. BTW I haven't done this personally yet but am thinking about it for a trip I'm looking into this year (which is why I know about it) so if this does work for you please let us know.
I assume that you wish to book the direct Rome-Paris night train. As the others have said, you will get the best discount fares if you book well in advance (up to 90 days) at either trenitalia.com or tgv-europe.com (a multi-language SNCF site). If you become one of the lucky few who succeeds in registering and booking on the Trenitalia site, well and good. You can book direct trains going FROM Italy TO France on tgv-europe.com, but as soon as you indicate that you wish to pick up your tickets in Italy the site will switch to Italian. Use Google translator to help you identify the fields in the booking process and choose to have the tickets mailed to your hotel. (Be sure to notify your hotel to be on the lookout for them.) SNCF does not allow you to pick up tickets at stations outside of France. Are you a party of two? If you're willing to share a couchette with strangers in order to save money, book a 4-bunk couchette rather than a 2-bunk one. Since all couchettes are the same size, you'll get more elbow room and luggage storage space in one that only has 4 beds pulled out. If you want privacy, splurge for a 2-bed sleeper.