Edit: Erm, stuck on the next bit with the gun turrets :/
That takes some doing. And this will practically solve the rest of the level, so warning to all:
***IF YOU DON'T WANT TO KNOW HOW TO BEAT ADVANCED 18 DON'T READ THIS POST FROM THIS POINT***
Right. As you enter that room, you have 4 turrets. You need to take out the two on the right hand side of the room. The closest to the platform you are on can be defeated by placing a portal behind it, stepping through and picking up/throwing it down into the goo. The other turret can be killed by taking the security cam off the wall, and then placing a portal behind the turret and throwing the cam at the turret to knock it off.
From there, head to the left hand side of the room and look to the far left top corner, place a portal up there, and a portal next to you on a wall. Look through this and look down, you will see a ledge/sticking out peice of wall, jump down onto this.
Look down, you will see a platform on top of the goo, place a portal as close as you can to the wall (where the two openings are for the button and the block platforms), and then jump down towards the floor, placing another portal on the way down. The momentum will throw you upwards, and strafing left should get you into the top most ledge.
Fire a portal back to where you entered the room, and leave one portal on the floor near the goo. Take the block and jump down into the portal, you then have the block back at the start of the room.
Repeat the above to press the button, then get back to the block. Take it through to get to the next part of the level.