ok...now don't call me a spoiler or anything, but if you absolutely cannot find that book,(and you have to get over that bridge to complete a required task,) try this one out...

Do ya know the cheat code to teleport over to the other side of the bridge ? You must have the patch 1.05 or 1.06, and in the the Icewind.ini file in your directory, find [Game Options], and type Cheats=1 in there. Then save your file, and go play the game, and use ctrl + tab to bring up a menu. Then type CHEATERSDOPROSPER:EnableCheatKeys();
just like that...then, move you cursor to the other side of the bridge that you want to be on, and make sure all of your party is highlighted, and do a ctrl + J
That will put you over there, but I suggest you only do this ONCE...It's no fun if you do it through the whole game.
I hope I got all that in there...and that no one ex-communicates me for that info shared !!!

sorry guys, I meant this to be an answer to a question posted earlier, and I went the wrong route...silly me...