you could use a bb code like what is in my sig, that is if you can make your own.
i am still having trouble with putting it on my phpbb2.1 forum because of all the little buggies running around.
but if you can use bbcodes to do it make it so only admin / mods can approve it
but this would be alot of work for just a sig, so nevermind.

but the bbcode is somewhat like this
[swf width=x height=x]URL to movie[/swf]

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