To detect flash plugin with include file and with AS, I, unfortunately don't know the technic how to manage it. But I'll give you a technic to detect flash plugin.
this method of detection flash is used only
with mx 2004.
make a html file for your main .fla file ( I describe it as index_real.html now)
1. take the main .fla file
2. choose file --> publish settings (html tab)
3. check the flash detection check box and then set up the settings for your movie ( see also other tabs).
4. (html tab) choose settings.
5. there are three gaps, which you have to modify for your movie ( I think you can manage with it). But the 2nd gap should be named differently than your .fla file. For example index_movie.html.
6. hit publish.
7. navigate to your flash page directory, delete the index_movie.html the and rename the index_real.html to index_movie.html.
Then, I suppose, your little detection plugin should work
I hope this helped you, but if I didn't understand or helped you, then give me a notice