[rebeldream]

any way to get past the green monsters and the bridge, 4th c.d.

[Bardos]

What level are your characters? If not enought to pass (not kill them --to kill them, you must be very strong), then try to rise 1-2 level and then try to pass the bridge.
You're refering to those insect-like creatures (can't remember name, now, sorry), right?

[Cadfael]

If you mean the ruins of the Firewine Bridge, Bardos is right... even though the plot is non-linier, you still need to be at a certain level to beat certain monsters with ease... if you are having trouble killing these monsters, you are definitely not ready for the dungeons on the other side of the bridge, this section is hard. The Kobolds keep regenerating.

...do you mean the drawbridge leading to the city of Baldur's Gate, if this is the case... the monsters are Ankhegs. You will need to use ranged weapons, and casting a haste spell on your party will help. When they burrow into the ground, move your party away, the Ankheg will surface close to where your group was.