When it comes to search engine optimization, flash sites are generally regarded as somewhat of a problem. The problem lies in the fact that the text content of a swf (flash) file is not readily available through view source like an html site. Instead the text is embedded into the swf and therefore is not indexable by the search engine spiders. This presents a problem for sites built using all flash.
Luckily, The developers at Deconcept have this flash SEO situation under control and have broken it down for the rest of us.

Here's how it's done: First design your page as if you aren’t using Flash at all. To do this, design an HTML page that contains a summary of what is covered in your site (the content). Then using "swfobject.js" you tell the browser to display the flash while the search engines actually index your HTML summary. This causes Google to skip the Flash swf files and only index the HTML (the content). When a viewer with a browser that supports Flash visits your site, they will only see the Flash content. This technique basically lets a 100% flash site be treated just like any other html page as far as search engines are concerned.

Heres a preview of the code that allows the search engines to index html content but display the flash instead:

<div id="flashcontent">

This is replaced by the Flash content if the user has the correct version of the Flash plugin installed.

Place your HTML content in here and Google will index it just as it would normal HTML content (because it is HTML content!)

Use HTML, embed images, anything you would normally place on an HTML page is fine.

</div>

<script type="text/javascript">

// <![CDATA[

var fo = new FlashObject("flashmovie.swf", “flashmovie", “300?, “300?, “8?, “#FF6600?);

fo.write("flashcontent");

// ]]>

</script>

For a full breakdown as well as the source files visit deconcept here: