Yahoo!7 Video makes it simple by providing the embed code that you can copy and paste:

• From the video page, click on the Share tab under the player and copy the embed code and paste into the markup of your webpage.
• If you want to display just the video thumbnail on your webpage, you can copy the thumbnail code under the Share tab and paste it into the markup of your webpage. When a visitor to your site clicks on the video thumbnail, they will link through to the video page on Yahoo!7 Video.