How exciting to be getting married in Italy! I've shot weddings in Italy a couple of times. The first was in Positano on the Amalfi Coast and the 2nd was in Rome at the Hassler Hotel where Tom Cruise and Katie Holmes and their guests stayed for their wedding at the Odescalchi Castle - I'm not sure if the Hassler has a space large enough for a 100 guest wedding, but it might be worth looking into as it is in a great view of Rome at the top of the spanish steps. I could also pass on the coordinator's info if you're interested. Here is a link to the Rome wedding:
Nathaniel Thompson's Photography Blog: wedding in rome, italy - melissa and jorge
And to the Positano photos:
Nathaniel Thompson's Photography Blog: regina and cory's wedding -the amalfi coast, italy