Please, create an html page first. Put a links on it to your Flash site and non-Flash site. Upload this html page to your Flash website's root directory.

Please, see how one of our customers have done this: http://thesuperweekend.co.uk/

Important. The "Flash" link should be directed to the starting page of your Flash website (in that case: http://thesuperweekend.co.uk/home/)

Very important. In order to not to harm your Flash site's SEO you should add the following line right in the beginning of your .htaccess file:

DirectoryIndex index.html