To embed YouTube videos in a wordpress blog follow these instructions:
Now you may cut-and-paste the required javascript into any blog post and they will render correctly.
If you drop the Embed script from YouTube into your blog post, the page will fail a HTML validator. In order to overcome this, drop the following code into your post:
<object type="application/x-shockwave-flash" data="http://www.youtube.com/v/your_video" width="425" height="350"><param name="movie" value="http://www.youtube.com/v/your_video" /><param name="wmode" value="transparent" /></object>
Replace ”your_video” with the id of your YouTube video. There must not be any end-line characters in this code - if you do, wordpress will insert paragraph tags and distort the post (text after the embedded code will be formatted badly on your page).
This solution is demonstrated on this post on my blog.