What, if any, nice restaurants will be open on Christmas Eve and on Christmas Day (for lunch)? Do I need to make a reservation weeks in advance or can I stop by upon my arrival 12/17?
The swanky hotels with restaurants will charge an excessive amount for Christmas dinners - 80 euro per person. Your best bet is to find a restaurant that will be open during these holidays. Some restaurants will be closed and the ones that are open will be busy. Maccheroni at Piazza delle Coppelle 44 is open 365 days a year. Pasta dishes are the specialty but they also have meat dishes. Since you arriving on 12/17 stop by the restaurant and take a look at the menu. If it will please your crowd make a reservation.
Be sure to check out the Christmas market at Piazza Navona and the Nativity scenes from around the world on display near Piazza del Popolo (http://www.rometravelcafe.com/events/details.asp?EventID=577)
In 2002, I spent Christmas Eve and Christmas Day in Rome. There were not many restaurants open on Christmas Day; however, I found one and it was crowded. I was alone, so they sat me easily. It was a fabulous meal. The restaurant is L'Arcano located on via dei Pastini just off the Pantheon (Piazza della Rotonda).
I was in Rome in June of 2007 and ate there again. My friends and I thought it was an excellent meal. Be sure to ask the price of an item before ordering and you will eat a reasonably priced meal.
As far as I could tell last Christmas - everything was open as usual on Christmas Eve.
I can't comment on whether you will find anything like what I would think of Christmas Dinner - the roast whatever and trimmings, but we ate in the "argentinian" (sorry don't have my books with me) area mid afternoon like we would at home. The menu appeared to be the normal menu for everyday and whilst it wasn't inexpensive I don't recollect that we paid extra for it being a holiday.