Want to take an afternoon tour of Vatican museums; arrive about noon; is it realistic to get to Vatican for a 3 pm tour?
What is the cost of the taxi?

I assume you are staying in Rome for more then just the tour? IF so you have to count in time to get your luggage (if you check), get it to the hotel etc.. (I don't think the Vatican is going to let you roll your luggage around) If that's the case I am not sure it's realistic (Baggage handling at FCO can be problematic)

If you are just going to the Vatican and back to the airport then possibly it's realistic.

It takes 45 min & 8 euros to get to Vatican by commuter train (take FM1 train to Roma Trastevere & then change train to Roma S.Pietro). Trains go in 30 min intervals (12:42, 13:12, 13:57, etc). Taxi will take approximately same time and will be around 45 euros.

Luggage delivery in FCO is not the speediest.

And the immigration line for non-EU nationals can be very slow.

A few years ago I flew into Rome from the US.

Scheduled arrival = 7:30
Actual arrival = 8:30 (weather delays at departure airport)
Passed through passport control = 9:30
1st bags arrived at baggage claim = 10:10
last bag arrived at baggage = 10:25

If you're arriving from another European city in a Schengen treaty zone country then you'd not have any wait at immigration.

arrive Rome on 5/15 and leave the next morning. only chance to see Vatican is afternoon.
Thought we should stay at airport hotel.
Suggestions?

If you arrive at noon, and take a taxi into the Vatican Museums, then you can easily make this - unless your flight (or luggage) is delayed.

I would plan up to an hour to get your luggage, although my multiple experiences at FCO usually run about 30-40 minutes. Then the ride to the Vatican is about 25-30 minutes by taxi. I would not attempt the trains or buses with your time restrictions. I've lived next door to the museums for 3+ years so we've traveled this route often - by all means of transportation.

If your luggage is not too large or numerous, you can check your luggage at the Vatican cloakroom and avoid having to go to a hotel and drop off (See their website for luggage restrictions - although one of my friends actually checked his guitar there!). If you are headed back to an airport hotel for the evening (NOT WHAT I WOULD RECOMMEND), then you could always leave your luggage at the FCO left luggage (see this link: http://tinyurl.com/Left-Luggage) and THEN catch the taxi to the Vatican.

But I'd stay in Rome at night - so you get to see this: http://tinyurl.com/rome-night and then fly out the next morning. Sounds like you're joining a tour, but if you go at it on your own, this article may help you: http://tinyurl.com/vatican-tips

As another option there is left luggage office in FCO (T3)
http://www.roninrome.com/transportat...luggage-please