Hi Roy...
There are a couple of ways. 1st way is to click the youtube button above the smileys and insert the text between the tags
[youtube]http://www.youtube.com/watch?v=t_8zVfUqAds[/youtube]
would give you this:
[youtube]http://www.youtube.com/watch?v=t_8zVfUqAds[/youtube]
You can also just paste in the part after /watch?= so in the above code it would be like this:
[youtube]t_8zVfUqAds[/youtube]
[youtube]t_8zVfUqAds[/youtube]
Hope that helps
Eric