The Sheraton Roma has a complimentary shuttle to two points in the city, it leaves on the hour starting at 7am, ending around 10pm. One stop is near the Termini (railroad station) and the other is close to all the tourist attractions. The drive takes about 20-25 minutes. If you like going back to the hotel for catnaps during the day, this may pose a problem. Since I preferred saving on hotel rates (Rome was expensive!) and the Sheraton Roma is on the cash and points list, I stayed there March 2005.
Linda