There is a walkthrough of that particular puzzle on your CD. The puzzles of the two chambers differ slightly. In one of them you have to walk around the rim of the chamber through all the fires flipping the two levers on the way. You must however not touch the middle fire or the puzzle will be reset. In the other puzzle you have to walk straight through the middle fire and back through the same fire again before the grate will open. I cannot remember which solution applies to which chamber.
That is the official version. I have tried it a couple of times and it does not always work.
What I found works best is running through the middle fire (which in both chambers opens the grate temporarily) with a crate in front of you. You have to pick a crate which passes under the grate lengthwise. (One cannot turn a crate around). After a few attempts you should be able to get it stuck beneath the grate. [img]smile.gif[/img]