Hi, It depends on how the flash page is gonna behave, it would be helpful if you provide more info about it, but in general you can set all up in the same template rendering the front-page, only handling the visibility of what you want to display.
Embed the code loading your flash in the same template rendering the front-page, wrap it in a div block and show it or not depending of whether first visit or not. Yeah, you probably would have to make use of cookies for that ;-)
You will eventually get better solutions that this one, just be patient, meanwhile you can give this a try ;-)