.flv is not natively supported in the major browsers, which means you either need to get the content in a different format, or you need to get an embedded player for .flv movies. The only one that I have personal experience with is Flowplayer, which has a free offering and is actually pretty damn good -
http://flowplayer.org. You will need to embed the player into your HTML pages according to their instructions in order to view the files in a browser.
Hope that helps!