From bowiki

There is a Videoflash extension to the wiki that allows us to embed Youtube videos. It is very straightforward to use. Here's how

Go to the video on Youtube and look at its URL e.g.

http://www.youtube.com/watch?v=3ChbigufBC8

The bit you want comes after the 'v=' this is the video code. In this case it is 3ChbigufBC8

In your wiki article enter the following videoflash markers either side of the Youtube code

<videoflash>3ChbigufBC8</videoflash>

and that's it. This will display the video full size in the article.

If you want to control the video size, you can do that using the following syntax

<videoflash>3ChbigufBC8|250|175</videoflash>

where 250 is the width of the player and 175 is the height of the player - adjust these variables and use the article preview to find a good fit. Please note the text does not flow around the video. You may find the article layout cleaner if you have the video code on its own line.