I'm excited for you and just a wee bit envious, even though we did the trip last year. It was fabulous!
Not knowing what tips and advice you already have here goes:
These observations are based on Sept 2008 Viva Italia.
I seem to remember 2 sections for Passport check (Rome - FCO). One was for European Union Passport holders and one was for non-European. Signs are in English so you shouldn't have a problem.
The person that meets you with the
ABD sign at the airport will be at the baggage pickup area. He will take you to the driver of your 'cab' (black Mercedes SUV). It was last year anyway. Hotel is a good 20-30 minutes away depending on traffic so if needed plan a restroom break before you leave the airport.
edit: Restrooms - Some of them have attendants and it is customary to give a tip. Some stand by the entry door and collect before you even go in to the stall. Not in the airport but I seem to remember it when we got off the bus in Orvieto and again at one of the restaurant's we ate at as a group.
ATM machines close to hotels in Rome and Venice and when you visit Florence.
Always ask before you order a meal if they take credit cards or you should have the cash on hand.
Rome lots of sightseeing. Shops near the hotel are 'high-end', designer. The street straight down from the Bernini is walkable and leads to the Trevi fountain area and Spanish steps. The street to the right and up has more hotels, restaurants and the American Embassy.
Orvieto ... shop all the ceramic stores first before you purchase anything. Different designs and quality in all. A lovely spot in the clouds, soak it up and sing Funicula Funiculare for me and others, again.
Florence - crazy, crowded but fun.
Venice - learn landmarks on the Strada Nuova and you won't get lost crossing the bridges.
Pack light weight clothes that can be washed in the sink and then air-dried.
Don't expect American hotel accomodations. Go with the flow and enjoy every minute of the experience. OK, I'm starting to get maudlin, enough. You get the idea ... you will love it!