I had a bit of confusion with this one myself as posting YouTube videos seem to differ on various sites and forums.
If it's a YouTube video you wish to show automatically on your profile page, follow this link:
http://www.yorkietalk.com/forums/yor...file-page.html
I got confused where it said 'enter your YouTube URL'. Can you believe, I actually entered the URL for my YouTube user page!!! Make sure it's the URL for the particular video you wish to show. I think you then need to type in the title of your video in the space beneath. The rest of the instructions seem fairly straightforward except for the part about the 'autoplay' at the end. Idiot yours truly got that confused as well!!!
If, on the other hand, you just want to post YouTube in this video forum, just copy and paste the URL as it appears. No alterations needed here.
Hope I've helped ... or have I caused even more confusion? Good luck and yappy video posting!