1) To find out if you need a visa check http://www.esteri.it/visti/, available in several languages.
2) If you do, you must enquire immediately (please, take the word immediately very seriously) with the Italian authorities in your country about the (long and detailed) list of documents needed.
3) Let Paola and Annalisa know, so that they may help you overcoming difficulties (based on the organizers' experience, there may be many) and provide you with links to necessary documents (e.g. you may be asked present a description of the Majorana Centre (can be found at www.ccsem.infn.it/em/history/index.html) and its location (a printout of "where is Erice" can be found under after FAQ).

To further emphasize the need to move quickly, a message sent by a participant in May 2008 is copied here below:

Regarding the visa, I think it was quite straight-forward except for the fact that the officers did not recognize some forms of evidence.
In my case, they did not see a confirmation of a hotel reservation (they issue visas only for the days you have hotel accommodation).
They are used to seeing an email confirmation like the ones you would get from regular hotels. So when I told them that this is a conference center, the officer had no idea.
And the Italian Consulate in San Francisco, CA, USA, recommended that we apply 30 days in advance and that is what I did.
But future participants should be aware Italian consulates in other countries/cities could behave differently.