That's a tough one. Supposedly the engines can look at text
inside SWFs but that's all a jumble, could be something bad through
ActionScript as far as they know, and there is no way to use the
tried and true HTML tag rules. Metadata is, I understand, pretty
much ignored nowadays (thanks spammers!). Your best bet is some
plain ole HTML text and solid incoming links. If someone knows
better let them speak.
You could set up your flash site inside hidden frames. One
frame can contain hidden html w/ meta data, H tags, etc. And the
other frame has your visible swf. This is also a good set up if you
want to embed a statistics rendering engine behind the scenes.
Unfortunately, nothing beats standards-based html sites for search
engines though, A?!