Portal 2-How to make a portal in Unity 3D

First of all, sorry for my english i am german.

After surfing in the internet i saw the upcomming game portal 2 and wondered how valve games made this portal thing, and my question is, how can i make portals in unity, where i can fly and look through just like in the game??? I know a bit of unity, but my talent is designing worlds in 3ds max, so i thought it would be a great thing to have the portal system in my world, so i'd have sth to play and not just to walk through. pls help me and thx for reading :)

here are vids of it:

http://www.youtube.com/watch?v=Bq2mZoKkqMw&feature=channel

http://www.youtube.com/watch?v=TluRVBhmf8w

The closest thing to Portal rendering (this is the name of the technique, and, no, it is not named after the game :) ) you can get in Unity is to use Render textures (Pro Only), get cameras to render into those the scene where you'd like your main camera to go to once it goes through the portal, and finally teleport the main camera there when you go through the 'portal' (use collision triggers).

http://answers.unity3d.com/questions/54955/portal-physics-effect

The game “Portalizer” for Android and Unity Web has Valve looking portals, and it’s really well made.