If you're flying into the Fiumicino airport ( there are 2 airports that serve Rome), you're probably better off taking the train into the Rome Termini station which connects with the subway sysem. It's a very good system.
If you're considering a day trip to another city, I have 3 suggestions; Florence, a beautiful city; Monte Cassino if you're a WW2 buff, but the most beautiful tour you could probably go on is going down to the Sorrento area and taking a tour along the Amalfi coast. You wont regret it. Absolutely beautiful scenery. I wouldn't advise renting a car for this part of the trip. Roads are narrow and you have to know which ones to take. You are probably better off doing this on a week day.
I'd recommend Venice, but it's just too far away.
They also have trips to the top of Mount Vesuvius, but they stop about a mile from the top, leaving you with a long walk and "occassionaly" they have a ice form near the top in which case forget about it, so that time of year, you're probably better off skipping it.
I was in Rome back in december and again in febuary. If you'd like more advice from me, just let me know.
Just one more tip on restaurants; if you like to have a few beers or a glass of wine, some restaurants charge up to $10.00 U.S. dollars for each, so you're better off asking first.
Just one more tip I promise. A lot of banks here charge a foreign transaction fee, each time you make a withdrawal (atm) or charge something. So you are better off making a larger withdrawal than several small ones.
Keep your wallet and your passport in your front pocket.
Be wary, especially in places like Naples. If someone makes you some kind of offer that seems to be too good to be true, then it isn't.
Have a good trip.