some observations.

vatican and colisseum are must sees.
vatican museum has a cd player you can rent that is pretty good.

colisseum has tours you can sign up for. check the times in advance.

a lot of things have long lines. check and see if there is a master musuem pass like in some other cities.

off the beaten path - there are tours of underground rome, meaning tunnels under the city. the current city is built on top of the ancient city.

also, the bourghese park is a nice place to check out.

also recommend dinner at the piazza navona area - hardly beaten path but more just an enjoyable place to stroll with locals and other tourists.

the pope used to have audiences in St. Peter's square on Weds, but you had to get a free ticket in advance. ask you hotel. I think you just ask for tix at the gold door in st. peters square that is at the end of one of the collonades. if you are catholic, you might be able to arrange a better interview with the pope via your local parish - an audience of perhaps 100 folks or so.