I found a simple solution, and I believe it is what you are looking for.
1. In Flash, go to File>Publish Settings
2. Click on the HTML Tab
3. Where is says Dimensions, select Percent
4. Though it is probably default, make sure the width and height are both set to 100.
5. Click ok then go to File>Publish
Now your movie should scale with the browser window.
If you do not have Flash, then you can simple work with this sample code below:
<object width="100%" height="100%" id="xyz" align="middle">
<param name="allowScriptAccess" value="sameDomain" />
<param name="allowFullScreen" value="false" />
<param name="movie" value="xyz.swf" />
<param name="quality" value="high" />
<param name="bgcolor" value="#ffffff" />
<embed src="xyz.swf" quality="high" bgcolor="#ffffff" width="100%" height="100%" name="xyz"
align="middle" allowScriptAccess="sameDomain" allowFullScreen="false" type="application/x-shockwave-flash"
pluginspage="http://www.macromedia.com/go/getflashplayer" />
</object>
Notice how width and height are set to "100%"? That's all you need.