I'm not sure if VBulletin supports "Jimbo Format" as we used to know it
I think you will have to change the "tone" of your message here.
Embeded Youtube videos should work on the other hand:
<object width="425" height="355"><param name="movie" value="http://www.youtube.com/v/pZ_Z_XG0L2c&rel=1"></param><param name="wmode" value="transparent"></param><embed src="http://www.youtube.com/v/pZ_Z_XG0L2c&rel=1" type="application/x-shockwave-flash" wmode="transparent" width="425" height="355"></embed></object>