I often get many questions about what to see and do in Rome. Below are some helpful links that will address just about anything you will need to know about visiting the Eternal City.
I highly recommend that you try to get reservations to the SCAVI (the excavations under St. Peter's Basilica). The email link is below.
The third link will direct you to the liturgical calendar of the Holy Father. If you plan to be in town for any of these liturgies or celebrations, you should contact the Bishops' Office for U.S. Visitors to the Vatican. Being present for a Papal Mass is a once in a lifetime experience.