I never used tim to connect to internet, but reading on tim website i've found this settings:
apn: ibox.tim.it
user and password: (nothing)
number: *99#
As i have understood, the ibox password isn't necessary to connect to internet. If i'm in wrong, in this thread
http://www.prepaidgsm.net/forum/index.php?showtopic=401 you can read how to obtain the ibox password.