If ToB is installed, press TAB and hold it down, and all the chest/crates-anything that can hold an item- will be displayed. Search through them in the D'Arnise hold and I found loads of Arrows of Acid/Fire to use.
None ToB Option: Search long and hard for all the things that hold items and you'll find something.
Also, Minsc, for some reason, was able to kill them using the Sword of Chaos when they were down. I think it is because after every sucessful hit it drains 1hp, which the Troll is probably not immune to.
DJG