I just purchased one-way tickets from Venice (Venezia) to Florence (Firenze). It was a snap. I thought perhaps it would be helpful to share some information regarding purchasing train tickets for travel in Europe.
To purchase tickets for travel from France to another country, I used the TGV-Europe website, www.tgv-europe.com .
Here's a tip for this website. When the home page splashes, it will ask you to select your country of residence. DO NOT, I repeat do not specify America. If you do, it will redirect you to www.raileurope.com, a partnered company for selling rail tickets, and you will pay a higher price. Instead, click on the UK dot, or if you do specify America, on the window that announces that you will be redirected to www.raileurope.com, instead of clicking the 'confirm' button, click the hyperlink that says 'continue on to www.tgv-europe.com.'
At www.tgv-europe.com , you can book all manner of trains (Eurostar, ICE, TGV, ES, etc.) to/from any country in Europe. Some reservations can be made with electronic tickets and some reservations must be made by receiving a paper ticket. I share this cautionary info, as I had an issue when I purchased my daughter's round trip train ticket from Germany** to Paris (Gare de l'Est), the only form of ticketing offered was a paper ticket requiring a German mailing address (the mailing was free, and the ticket was mailed to her German address without incident.)
**(She refused to fly the itinerary because Lufthansa - the cheapest carrier from Germany to CDG - requires a car set buckled into the airline seat for small children and it is a MAJOR hassle.)
For tickets for travel in Germany, you can also use the deutschbahn website at www.bahn.com/i/view/USA/en/index.shtml. On this site, if you specify your country as residence as the USA, you will not be redirected.
For train travel in Italy, I used www.trenitalia.com, clicked on English in the upper right hand corner, and it was a snap. When specifying origination/destination cities, even on the English site, you need to know how the city is spelled in Italian (ie. Venice is Venezia, Florence Firenze, etc.).
Only once have I purchased a eurail pass, but I think I would have been better served on that trip to have just purchased tickets separately. If you are doing heavy train travel, then it's great. To learn more about Eurail passes, go to Rick Steves' Eurail Passes.
Here are some additional links regarding local transportation:
Busses - From the airport, City Bus number 5 takes you to Venice, number 15 to Mestre. An inexpensive option, but you probably don't want to use it when you have a lot of luggage. Like most local buses in Italy, buy a ticket at a tabacchi (tobacco store) or newsstand. There is one at the airport.
For Vaporetto information - www.actv.it | Actv - impresa e territorio, il valore dei fatti
For the Alilaguna boats to/from Marco Polo Airport and Venice - www.alilaguna.it/?lang=en
Tips for taking a gondola ride - Venice Gondola Rides - What to Know about Gondolas in Venice Italy
www.ratp.fr (this site has been my best friend when visiting Paris)
If you have any other information regarding rail transportation in Europe, please chime in. I will add the appropriate tags to the post.
Thanks, and happy and safe travels.