File > Import > Import Video... Flash actually supports .mov files, so you won't even have to convert to .flv if you don't want to.
General notice: from now on, I would like to ask everyone to put [AS2] or [AS3] (corresponding to the version of actionscript you are using on your project) in front of their post titles when the question is actionscript related! Please help us help you faster. Thank you.