I am traveling solo for the first time to Florence, Italy on USairways and connecting in Frankfurt, picking up a lufthansa flight for the rest of the trip. Will I need to reclaim & check baggage, go through customs again, etc? I have about an hr and 40 min between flights. Thanks for any light anyone can shed on the situation!

You will not have to collect luggage, you will have to pass through immigration & security checks. Don't dawdle as it can be guaranteed that where you arrive will be a long way from where you want to be.

Allow at least 2 hours, as you need to go to a different terminal. Lines at passport control can be long but usually go pretty quickly, its getting to them and then into the other terminal that seems to take the time, and in some cases you end up going through security 2 times instead of one depending on your departing gate.

You wont go through customs at all until you reach Florence.
I would have no concern with 1hr 40 min layover.

USAirways and Lufthansa are both star alliance members so in addition to having your bags checked all the way through you should be able to checkin for FRA-FLR leg at your origin in the US.

Thank you. I will definitely ask again if that's possible. It seems that every time I call USAir I get a different answer.

If you purchased it as one ticket then there's no way you will have to claim and re-check your luggage. Even if you didn't purchase it as one ticket there is surely a bag check agreement between these two airlines.

Last year I flew to Italy with a stop in Paris. I did go through a line in Paris where they stamped my passport as entering the EU through France, then the flight from Paris to Italy must have been treated as a domestic flight as I did not go through any type of checks when I arrived in Italy. Maybe this is because both France and Italy are in the EU? If that's the case then the same will apply going from Germany to Italy.

But in any case I did not have to claim and recheck my bag and neither will you.