The TARDIS doesn't have any weapons, although it defences are invulnerable as long as you remember to keep the shields up (I read somewhere they work by putting the TARDIS a milisecond out of time with the attacker, nullifying any attack). There were BATTLE TARDISES during the Time War, though, which presumably had weaponry (unspecified, but one assumes that it's pretty heavy duty and probably time-related).
