Rome to Venice: Train or Car?

Absolutely train. Much faster, cheaper, no stress. Book tickets ahead on Trenitalia website. Check train schedule on Deutsche Bahn website. It's easier to read. Click on Travel Tips on this website to learn more.

Driving out of Rome will be a nightmare, driving into Venice is impossible. A High Speed Train goes from city centre to city centre, a lot faster than you can drive and cheaper.
You can't book tickets for Italian train on the DB website. For train times AND bookings in Italy, use the Italian Railways site: http://www.trenitalia.com/ You need to enter the correct names of the stations, Roma Termini and Venezia S. Lucia. The train takes 3h45, there is one train per hour.
For long distance trips like Rome to Venice, it is cheaper to decide which train you want to travel on and book in advance (2-3 months). The cheapest fare is €39

There is also an Italo train for that journey.

Does the train arrive in Venice and we'd have to take a water taxi to the old town? I remember the airport was away from the main part of Venice....

Alexandra,
Venezia S. Lucia station is right in the centre of Venice, on the Grand Canal (Venice's Main Street). It is further into Venice than you can go by car. You get off your train, walk out the front of the station and the Grand Canal is in front of you. It is one of the great "wow" views of Italy.
Click here for a photo I found, the station is the white building on the right. You can then walk or take a water bus to your hotel.

Absolutely train! Fast and inexpensive. You can book through RailEurope.com easily, or just purchase your ticket at the station. Have a great trip!

Great! Sounds like the train is the way to go. If I can ask another question: I'm used to taking trains all over Germany. Are they in Italy similar as far as their punctuality, ease of use, etc...?

Answering your last question, as of a few years ago, Italy trains were not up to standards of the German trail system in terms of punctuality.
Perhaps this is changed in the last few years, but I doubt it.

Usually fast trains are pretty much on time, otherwise because Italy is different than Germany, trains are sometimes not on time, sometimes there is a strike, to buy ticket at the window takes usually quite longer, simply it is Italy and we don't expect it to be like Germany.

To know about Italian trains, ask Tim Parks

http://www.amazon.com/Italian-Ways-Rails-Milan-Palermo/dp/0393348822

Alexandra, I would say the difference between Italian and German trains reflects the difference between Italy and Germany.
Italian trains are less punctual than in Germany, and sometimes seem a little bit chaotic. Second class coaches can be a bit less well 'cared for' than in Germany, and regional trains can sometimes be a bit full. But they are just as easy to use and will get you from A to B in reasonable comfort.
Trains are cheaper in Italy than Germany, which can explain why second class regional trains can get full.

Alexandra,

I would also most definitely advise travel by train. You'll be travelling on high speed trains on that route, which travel at up to 300 kmH, so this is a MUCH faster and more efficient method than by car.

There are two options you can look at.....

1. Trenitalia - use a Freccia train from Roma Termini to Venezia Santa Lucia (direct, 3H:45M). Tickets for these trains have compulsory reservations which are specific to train, date and departure time. If you can commit to a specific departure time, you can pre-purchase tickets online at a considerable discount. However, note that the least expensive Super Economy tickets are non-refundable and non-changeable, so choose carefully!
2. Italo - you could also travel via the competing Italo high speed trains, but many of these depart from Roma Tiburtina station (which is not really much of a problem).

If you want to pre-purchase tickets, you can do so either on the Trenitalia website or at italiarail.com. Tickets for Italo are purchased on their website.

The trains in Italy are generally as reliable as those in Germany, although there can always be a strike (those are usually announced well in advance). You may enjoy watching THIS short video covering train travel in Italy.

I think the best solution would be to go by train either on Italo.it website or trenitalia.it website. You can buy directly your ticket from these website using your credit card, and price is clearly indicated.
DB does not give you this possibility if it concerns travelling out of Germany.

On trenitalia, fares are cheaper on Tuesdays, Wednesdays and Thursdays.
In the summer, There are also interesting fares on saturdays for families

Thanks for the helpful suggestions and the video link!

We always use the trains. You can't drive into Venice anyway (unless the rental company rented you a boat!) and Italian drivers are outrageous and scary. You can get a Eurail Italy Pass which will take you by train all over Italy. www.eurail.com/eurail-passes/one-country-pass/italy The trains are wonderful- let them do the driving while you enjoy the view.

Alexandra. no way buy a rail pass!
You have only said you want to make one rail journey. Rome to Venice. If you book in advance, the cheapest price for a normal ticket. is €39.
The shortest duration pass costs €166 for 3 days (€55 per day), plus you will still have to make a reservation on your chosen train, and that costs €10.

Good to know! Thanks.

I think some of the trains are even made by Ferrari! Or at least have their branding.