How to convert a .flv to a .swf

You can't do a direct flv to swf conversion... an flv is a video file and a .swf is a Flash file.

What you can do is import the flv into a swf. Of course, this assumes the .swf has code/components that are set up to play the flv file. There are a few commercially available products that will do this for you... searching "flv to swf converter" on google will give you some results.

Depending on what it is you're trying to accomplish, the better option might be to keep the flv as a separate file, and use a .swf to play the file from it's location. If the idea here is to play an flv from your website, see the JWPlayer page for some options (JWPlayer is a widely used, open source Flash video player) http://www.longtailvideo.com/players/jw-flv-player/