Possible itinerary in Rome

Looks good to me. You'll be able to add things to your day as they are light. Make sure you visit the Pantheon as it's just a 5 minute walk from the Piazza Navona and on the way to the trevi fountain. You'll either have to walk or cab it from P. Navona to the colosseum. It's about a half hour walk but you'll be doing a lot of walking that day. Same for the Borghese gallery. I would take a cab and then the metro to get to St. Peter's. Be sure to make your reservation for the Gallery as you can't get in without one. Donna

The Borghese does not take much time to see. You might want to make a reservation for late afternoon or early evening your first day. That would allow you to see St. Peter's and the Vatican museum in the same day and not give you too many art museums at once. I'm not convinced that the best use of time is to try to see Ostia Antica over other sites in Rome. You could see the Colossem, Forum, Pantheon and a lot of the sites in between in a nice walking day (e.g. Victor Emmanuel, Spanish Steps, Piazza Navona). You could also add Capitol Hill and associated museums next to the Forum. Have fun.

Agree with Rob, save OA for another trip. Takes too much of your limited time.

I'm a HUUGE fan of Ostia Antica but I'm a bigger fan of Rome, and I would have to agree that going to Ostia is probably not the best use of your time on this trip. If for some reason you're just overwhelmed by the city, though, you could always have it in your back pocket as a day trip.

Barbara, Glad to see you posted your itinerary, since we didn't connect by email. Our 3 day tour includes much of the same, but we decided to axe Ostia Antica due to the limited time in Rome and the amount of time needed for Ostia. Here is our general plan, although, my best advice, is to be flexible and be willing to make changes on the go. Arrive late Tuesday afternoon from Montepulciano. Staying in the Piazza Novona area. Wednesday AM: Quick stop at San Pietro in Vincoli on the way to 9:30 private guide tour of Colosseum, Forum, and Palatine. Wednesday PM: Capitoline Hill, Museums (as time allows), and Santa Maria in Aracoeli. Head back to hotel area via the Jewish Ghetto. Dinner in the Piazza Navona area. Thursday AM: Campo de' Fiori, Pantheon, Palazzo Doria Pamphilj, and Trevi Fountain. Thursday PM: Museo Borghese (3 PM reservation), followed by Piazza and Santa Maria del Popolo, and Spanish Steps. Dinner in Spanish Steps area. Friday AM: Private guide tour of Vatican Museum, Sistine Chapel, and St. Peter's.
Friday PM: Cross the river and stroll south on Via Giulia to its end , crossing back into Trastevere. As time allows, see one or both of Palazzo Corsini/Galleria Nazionale d'Arte Antica and Santa Maria in Trastevere. Dinner either in Trastevere, or back near hotel near Piazza Navona.

Two things: 1) get on those reservations asap! Borghese fills up and that underground one is filling up fast, check out my post about paying no more than 9.00 Euros for the underground tour, lots of ppl have posted on it and have given really good info, specifically Amy! 2) Be prepared, as ppl told me to be, to not get all done that you want too...it's LOTS of walking in Rome and as a newly engaged couple at 29 & 30yrs old, we had to cut things out b/c our feet hurt SOOOOO bad!! Good luck with your questions, the ppl on here are amazing and will definitely be able to help you really narrow down your days!!