The best approach to embed a SWF into an HTML page is to use SWFObject.
It is a simple open-source JavaScript library that is easy-to-use and standards-friendly method to embed Flash content.
It also offers Flash player version detection. If the user does not have the version of Flash required or has JavaScript disabled, they will see an alternate content. You can also use this library to trigger a Flash player upgrade. Once the user has upgraded, they will be redirected back to the page.
An example from the documentation:
SWFObject dynamic embed - step 3swfobject.embedSWF("myContent.swf", "myContent", "300", "120", "9.0.0");
Alternative content
A good tool to use along with this is the SWFObject HTML and JavaScript generator. It basically generates the HTML and JavaScript you need to embed the Flash using SWFObject. Comes with a very simple UI for you to input your parameters.
It Is highly recommended and very simple to use.