Sorry to hear you are having difficulty setting up Tre wireless with your iPad. Hopefully the suggestions here will help you.
I'd like to report that I just returned from two weeks in Italy and found that using Tre was flawless.
Although some people suggested that there is a Tre store at Rome airport, I did not attempt to go there because it is actually in a secure area in a different terminal from where I landed. I didn't think it would be possible to exit my terminal and then re-enter a different one since I had no boarding pass for a flight there.
Instead, I mapped out the nearest Tre store to where I was staying in Rome: located at Via del Corso, 417, 00186 Roma. This is in the general area of the Spanish Steps. I requested a SIM with one month data (3 GB) and paid cash in Euro (cost was 8 Euro, not 5 Euro as some others have reported here). I showed my passport, and asked the Tre store clerk to install the SIM and set it up. I was concerned that since I didn't have a laptop with iTunes, there may be trouble if I try to set it up. The clerk did not connect my iPad to any computer at all -- it took only a few minutes to complete the transaction and the SIM was activated and working immediately.
I had zero network problems anywhere in Italy. I traveled to Rome, Florence, Venice, and some pretty remote areas near where we stayed in Tuscany. Tre worked perfectly. In fact, having the iPad with Google Maps was a real life-saver as we had rented a car and used it to track us as we drove. After two wonderful weeks in Italy, we took 3 days to hang out in London. Used our same Tre SIM card to access the network there via roaming. No additional charges, again worked perfectly.
I couldn't have been happier with with performance and the price.