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I don't think you can do that - never seen it done at least anyways - and sounds like a bad idea as I would not want flash clogging up my email.

best bet might be to create an html mail and run a little animated gif - which will be blocked by gmail initially and the user will have to click 'show images'.
 
Don't know that this would be useful to you, but most people don't realize that you can embed Flash (as well as QT) into a PDF.
 
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