I have been trying to get an answer to this with my Friend Egidio Bruno at
Agency Services -SCALEA- - Home (bill paying service) and he has found the following:
Taken from this document:
http://www.agenziaentrate.it/ilwwcm/..._pf_estero.pdf
Ok the situation is this (today, hopefully it won't change too quickly):
The need for foreign residents to make a declaration for income on their home in Italy is neccessary if the follow criteria is met:
-The property generates an income (ie is rented)
-The rendita of the property is high enough, the calculation is complicated but basically if your rendita is above 358euro.
The rendita catastale can be found on your deeds or visura catastale.
Luckly for most people the rendita of their property will not arrive at 358 therefore they don't need to make a declaration for IRPEF. However if your property does have a rendita which is 358 or above then you will need to make a declaration for IRPEF and pay the nominal tax (in Italy we are not just taxed on income, but potential income

)
You can make the declaration by going to the agenzia delle entrate where they offer assistance to non residents for filling out the modello unico. Or you can go an see a commercialista or accountant (easier but costs money!).
DISCLAIMER
Lastly I want to finish that this information is provided in good faith and I wil not be held responsible for an errors, as it would be impossible for me to be 100% that this is correct as things change every 5 minutes. So if you get any problems as a result of this information, don't sue me basically!