Find your clip on YouTube.com or another video
hosting site. You need to make sure the clip
you choose shows the Embed code. Highlight this
code and copy it (
-c
on a Mac, or ctrl-c on a PC).

Go to the week's Discussion Forum, and click Reply to my post or that of one of your colleagues.
Click on the Toggle HTML logo in your tool bar (it appears after you click Reply).

Paste the code into the box to embed your video
clip right into the post. (pasting is
-v
on a Mac, or ctrl-v on a PC).

Be sure to click the button to post!
You are not limited to YouTube. Many other sites now provide embed codes for video clips, animations, etc.