Simply go to YouTube and 'cut and paste' the web link of the video you want to embed into the forum message.
EXAMPLEhttp://www.youtube.com/watch?v=eyBTJKrVxiTHighlight the address and click the YouTube icon above the message box. You link should now look like this:
EXAMPLE[youtube.]http://www.youtube.com/watch?v=eyBTJKrVxiT[/youtube.]Publish your message.