Add a new layer and design your ad on top of this video. (box with text or animation, etc.)
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Add a new layer and create a white box, change the fill alpha to 0.
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Use this tutorial that shows you how to do basic linking using as2 and as3 on the white, transparent box you just made.
http://forums.adobe.com/thread/113171
or use the link posted above for the tracking link and you should be good
Best of luck