I read a walkthrough bit that said

"The trick here is to walk over the central fire (the one directly facing the portcullis) and then walk backwards through it. After you have done this walk around the edge of the room and slip through the gate. "

The last time I checked, a rectangular room has two "edges". I have no idea what direction you're supposed to walk over the fire originally (toward the portcullis? tried it) then afterwards, do you go right, left? wtf.
do you walk over the multiple fires that hurt you as you "walk around the edge"? grrr. I tried a lot of things, the first quest should not be this frigging hard

S P O I L E R S :


Go back and get a treasure chest, take it back downstairs and push it in front of you. After going thru the center fire (BTW, it replenishes your HPs, it doesn't hurt you), *run* thru the gate with the chest in front of you. The gate will come down on the chest and spring back up, long enough for you to get thru. HTH. Have fun!