Cheers Oizo & Lyndon!
Just one of the bombs will blow the tower as long as you throw it in the right place! Actually anywhere in the general direction of the tower will do!!
I am writing up my walkthrough at the moment which I hope to get posted on APi in the next couple of days so if you get stuck any more, hopefully it will help.
Or just ask!
Enjoy the rest of the game and when you finish it, let the credits roll because after they have finished, there's some more you can do with Ico!