Rooting and RUUs are different things. You can flash an RUU without rooting, and indeed an RUU will unroot the phone.
If it's a TIM handset (Italian) then you'll need a Goldcard in order to flash a stock WWE (World Wide English) RUU to debrand it. The possible exception is the android 2.3 upgrade RUU, which works on many networks without a goldcard. I don't know whether that includes TIM, but if not it should just refuse to run (cid error) so it should do no harm to try.