Here's the code you should be copying into your post, in order to embed videos that play when clicked. Find this on the right-hand column of the YouTube video page. [note that after you copy the embeding link, you should click on the "Edit Html" tab at the upper right corner of the editing window before pasting].
To make your video fit better, change all of the widths in the embed code to
Update: To get the movie to fit as best as possible, you'll need to change the height, too. Try a proportion calculator. Enter the embed tag's current dimensions for the original size, and enter 525 for the target (reproduction) width. Press "Calculate" and replace the current dimensions with the target dimensions in the embed tag (in both places).
