Stuck on last leven of Portal

[o R 0 G U E o]

I must be being dim - but I'm stuck on the last level of Portal. I've got to the part where the platform is going into the fires for the intentional murder and can get to the end platform where they say - lay down your device and lay down face down and wait for your party. But but but - sod all happens - and despite trying shooting portals everywhere I am just stuck. Argggg. What a great game.
Any help to get this out of my head gratefully received?

[CAM3L]

Hey Rogue,

This video might be useful ;D

uk.youtube.com/watch?v=jWdkMNKbRdg&feature=related

[o R 0 G U E o]

Hiya Camel. Thanks for the video link. That helps tremendously. ;D