Flash stack

1,The simplest method :----------
When designing a webpage, you can move the navigation plane down. Isn't it enough to put the animation on it?
2,It's a bit difficult for you :-------------
Open the fla file of the navigation, create an empty mc on the last layer, name it "mc", and write the code on the first shot:

LoadMovie ("background .swf", mc)

Finally, you must put the background animation file and the navigation file in the same directory.
3,The method is more difficult than yours :-------------
After cracking the background animation, I slowly put it into the fla in the navigation, and I made it again.