On adding video to a web page using Fireworks, you can't do that. Fireworks is designed to create graphics for web pages, it is not designed to create actual web pages. Fireworks assumes that you will be interfacing with Dreamweaver to create the actual web page, so you will need to place any multimedia using Dreamweaver.
But, you can use Fireworks to lay out the page so that it is ready to accept video in Dreamweaver. What you need to do to make sure that your layout is not affected is to put in a placeholder image using Fireworks that is the same size as the video you want to insert using Dreamweaver, that will create a properly sized place for the video to go. Then simply replace the placeholder image with the video in Dreamweaver. If you open the Fireworks Help file and do a search for Video you will get step by step instructions on putting in a placeholder image.