Thanks to Datahopa for finding this and pointing me in the right direction :)
You should now see a YouTube button when you make a new post - it's under the B or bold button.
Just click that and between the tags put the YouTube code.
Getting the code at YouTube is easy - just click on their 'Share' button and copy the link it gives.
So you should end up with something looking like this :
[youtube]http://www.youtube.com/watch?v=FzRH3iTQPrk[/youtube]
Which will show the video like so ....
http://www.youtube.com/watch?v=FzRH3iTQPrk
This one isnt cute but quite funny.
http://www.youtube.com/watch?v=dL2m3lAD4U4