Set the dimension of your flash page to 750x410px. In some cases you're safe to go 780x480px.
This ensures that users on 800x600 display resolution will be able to view your page without having to scroll vertically or horizontally.
The reason for that is because you've got to take the top address and navigation bar of the web browser into consideration as well as the bottom toolbar. Therefore, the actual viewable portion of the screen is normally 780x480px
You can always switch your resolution back to 800x600 and expriment.