I know I am supposed to use the sign, and the nail, to cross the bridge, but it's not working...HELP!! <img border="0" alt="" title="" src="graemlins/woozy.gif" />

I almost gave up on this part too. If you are on the correct bridge you should be able to walk about 3/4 the way up. Then part of th bridge will fall away and then .............

SPOILER*
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This is tricky but as you face the ruins get the 2 boards from your inventory...you know the ones you took from the "Danger Sign".(Uh...This would be a good time to save your game) and place them on the upper right side of the bridge that you are on. When placed correctly the boards will "stradle" between the two bridges. Then you can climb up onto the board (well, Brent will anyway!) alternate the boards as you step across the bridge.
(Very similar to Dracula: The Last Sanctuary)Pick up the first board and place it down in front of you. Step on it. Turn around and get the other board. Place it in front of you. Keep doing this action until you've crossed over the bridge.