Can we use our American system in Italy? The rental car companys charge big bucks to include it in the rental.
You need to have western Europe maps loaded. If you do, your GPS will work fine in Europe. If you don't currently have the maps, you most likely can buy them from the manufacturer.
If you have the maps, it'll work fine. Satellites are satellites; lat/lon is lat/lon.
You can usually buy an SD card or digital download from Garmin or TomTom probably Magellan too.