You can easily stream YouTube or Vimeo videos with Presenter by Worship Extreme.
Start by creating a new cue and set the background type to Web Video. Click Set Video and paste in the desired video URL and click Save. Next time the cue is fired, the video will start playing as your cue background.
Some videos that play on youtube.com may show a "Video Unavailable" message when used in Presenter. This is controlled by the YouTube video creator/uploader. They may mark their videos as "youtube.com only" which will prevent the video(s) from being played in external programs such as Presenter.
To play a USTREAM video fullscreen, open the video in a browser and choose the pop-out icon in the bottom right of the player. In the pop-up window, copy the URL and paste that URL as a web page cue background in Presenter.