C# version of yield when loading a scene?

I found this example in the Unity reference manual, but its only Javascript.

function Start () 
{
// Start streaming the data file
var stream =
  new WWW ("http://www.unity3d.com/webplayers/Lightning/lightning.unity3d");

// Yield until stream is done
yield stream;

// Load it!
stream.LoadUnityWeb();
}

I’ve tried to convert it into C#

But I cant get the stream and the yiekd to work? what am I missing here?

I would like to be able to load other unity3D files from a webserver to add new levels.

Well, the second example is somewhat enlightening. Basically, what you could do is spawn off a web coroutine that uses this:

while (!stream.isDone) {
      yield return null;
}

It might be possible to yield return stream though, have you tried it?