in the page that holds the flash movie, you can start a session like this... Then you will want to create a variable to store whether or not the flsah file has been seen...
<?php session_start();
session_register('flashSeen');
?>
Then from within your Flash movie, you can set the variable "flashSeen" to true or 1 or yes or whatever value you want to use to track it by using the Actionscript command "loadVariable"
You'll want to load your variable from the page that the Flash movie is on, and append the URL with "?flashSeen=True"
Then it is simply a case of putting logic in your flash movie to do some thing like
if (flashSeen == TRUE) then gotoAndPlay(3)....
This is of course not the actual code, but mayb ethis will help you work thorugh it a bit?
Also, I would recommend moving you intro back to at least frame 3 and putting the logic for choosing the frame to frame 2... Flash movies dont always seem to do what they are told on Frame 1, especially if there are a lot of things loading or animating.
Hope this helps.