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One thing you can try is putting text in some CSS z-layers and playing around with the relative positioning to put the text behind the Flash movie. Definitely not a perfect solution - but Flash is a pretty big handicap to overcome from an SEO standpoint.
The HTML that holds your flash object and embed code should simply have a descriptive <title> tag and a solid paragraph (4-5 sentences) or two that describe the use or value of the flash movie to the user. Use language similar to what you'd expect a person to type into a search engine if they were looking for what the flash movie provides.
Ensure that any navigation links inside your Flash movie are duplicated with appropriate anchor text in the HTML pages.
Because the paragraph, title, and navigation are relatively short and straightforward, there's no need to hide it from the user -- they'll probably appreciate having something on the page while they're waiting for the flash to load. ;)