The obvious tags are [youtube] or something similar.
The replacement should be
(Click here to show video)[/url]{param}" type="application/x-shockwave-flash" width="425" height="350">Click play to begin.
The bit in red might want changing to whatever IPB requires in there. Might be {variable} or something. But as you can see that is where the piece inside of the tag will end up. Like this [ youtube ]http://http://[/ youtube ]
You could change the yellow bit as well, James.
And that is it!
To make a post with this you'd need to grab this bit from youtube
http://www.youtube.com/v/5MooE3RQgY4" type="application/x-shockwave-flash" width="425" height="350">
You'd need to grab the bit in pink and stick that inbetween the tags. The entire thing will produce the text that is in yellow as a link, which you click, then it reveals the video on the same page. I'll admit to nicking the code for the hiding bit from a spoiler tag.
I do hope this works
![Very Happy :D](./images/smilies/icon_e_biggrin_dark.gif)