I found the archers to be more of a problem than the poison. If you step off the path for a moment, you get poisoned, but it wears off fairly quickly, and though your health drops, it doesn't kill you outright. But the archers with exploding arrow can drop you real fast. I went in slowly and carefully; I had no bow at the time, so I would try to get the attention of one at a time and lob a magic missile at it, then back up the safe path a bit until I could step sideways without getting poisoned and dodge their fire. I found I could always retreat to just after the first stairs until I got to the point I had to jump the middle part (which only left the boss to deal with, and he was easy enough to avoid until the end. If one charged me, all the better, I just made sure I had room to maneuver and took it on in my "safe" corner. I killed them all one at a time that way, and it took a long time, but it worked. When you don't have enemies to worry about, it's easy to stay on the safe path.
First thing I did after was get a decent bow, because magic missile is just lame if you have a non-mage build.
