1. Go to the youtube video on youtube.com.
2. Click on the "Share" button under the video, and then the "Embed" button.
3. Checkbox "Use old embed code"
4. Select the video size box: 640x510 or 960x750 (just don't go higher than 960 width)
5. Right click on the code box (<object width="960" height="750">) and click COPY Or left click on the code box and press CTRL-C (or COMMAND-C on mac)
6. Go to Ax and start a post.
7. Right click within your message where you want the video to appear and select PASTE or press CTRL-V (or COMMAND-V on Mac)
8. You will see some code in your post that looks like this...

<object width="960" height="750">
<embed src="http://www.youtube.com/v/BlpOCUq3nYo?fs=1&hl=en_US" type="application/x-shockwave-flash" allowscriptaccess="always"
allowfullscreen="true" width="960" height="750"></embed></object>

9. Click PREVIEW POST to make sure the video displays properly in your message.
10. If it looks okay, then click Submit Post.

Let me know if you have any questions.