Just a quick note to save you a lot of money - before you leave the US you need to get an IDP at the AAA for around $20.
Don't forget your DL.
Also before you go read up on Italian driving laws - there are a number of gotchas.
Learn about how to avoid ZTLs. Understand that cameras patrol the areas that need patrolling - it is unlikely you will be pulled over for speeding but the camera will get you.
If you get a ticket it will be sent to the owner of the car - the rental company. So they don't have to pay your fine they provide the details of the driver to the police who - eventually - mail you the ticket which will increase over a period of time. The rental place will charge your credit card around 40€ for supplying your details. You will have agreed to all this in your contract.
Don't drive or park in a bus lane. Don't speed. Learn to recognize no entry signs and one-way signs.
Many credit card insurances are not valid in Italy. Certain insurance is required by Italian law.
Watch out for motorinos, pedestrians and bicycles.
Plan ahead - use your GPS or map app, and be prepared. A word to the wise is sufficient...
enjoy