Even if we figure out how to put YouTube videos and pictures into the forum, I recommend something else.
The first option is to get a WaterTribe blog going. Then post videos, pictures, long posts, etc. in that blog. If you already have a blog setup, consider importing it to a WaterTribe blog and see how it goes. If you decide that the import is too difficult or you don't like it, just let me know and I can dump the WaterTribe version.
Once you have a blog running, you can post short excerpts to the forum with a link to your blog.
If you want to post a YouTube video or picture without using a blog, just post the link in the forum.