Is it possible to stream a YouTube video in Powerpoint for Mac 2011?
There is a very simple method by using the Hyperlink command in PowerPoint.

You can Hyperlink any object in you Presentation. 

Here is a sample how to do it for this sample presentation I made.



Now Right Click on the Text Box "Streaming You Tube" and select Hyperlink.

In Hyperlink paste the link to the you tube video.

It looks like this in my example.