Yeah, the area below I am trying to figure out at the moment.

It took me a while to realize that you can simply *place* the rocks through the grate. I was throwing them :\

Still not clear on how to solve the rotating teleporter chamber:S

I see the pressure plate to the right corner -
And I can't get into the left area...

Yeah - I'm stuck... big time ;)

[Edit:] OK, I ran to right, throw rock to the left onto pressure plate.
Then ran over to the left area, removed the rock and found the metal door.

All I did was getting stuck in a new area LOL. I like this game but it is frustrating sometimes :)

[Edit 2] Ok, doing the above: Stand on central trapdoor - ready an item to drop/throw. Step west with portal passing - drop item, back to central then run straight through the now open gate. There is just enough time..

Pewieee!! :)

Make sure you are encumbered and you can to stsand next to the doir and drop through the grate, but if I remember correctly, this isn't enough time for the door to open before teleporters come around again. But the above should work, my second party made it. Try not to do any unnecessary turns on the way - might help.
Good luck and I hope you beat this puzzle soon!