Forum Moderators: open
I think that we can split this into two themes.
(1) The speed and size of your flash movie. It sounds as if your flash could do with a lot of optimisation. Are you using a lot of images (rather than vector graphics built in Flash)? Are you using large sound files? My personal take is that if you are going to build your site in Flash then you should optimise it for ease of download (and quick rendering) as much as possible.
(2) The common practice seems to be to offer the user the choice of a "High Bandwidth" Flash site or a "Low Bandwidth" HTML site. This can be done at an initial launch page. So, yes, it is easily done to have a Flash site and an HTML site running side by site - or more accurately, branching from an initial point where the user selects their preference.
HTH