WebEasy pages don't have a way of telling whether a flash movie has stopped playing, so there isn't a "perfect" solution. However, one alternative is to use a page transition to advance to the next page after a certain number of seconds:
1) In WebEasy, go to the page that has the flash intro on it.
2) Click the "Page" button in the left toolbar then click the "Transition" button in the top toolbar.
3) Check the "Advance to next page" box, and enter the number of seconds to wait (this should be the same, or slightly longer than, the number of seconds the flash movie goes for).
4) Click OK.