you can export as a quicktime movie and then go from there. I don't know if there is a export option for mpeg 2 - at least not for the mac version of Flash.
This is kind of convoluted, but assuming you are exporting from Flash or Director, export into Quicktime or Quicktime Video (depending on preference) and then use ffmpegX to encode into MPEG-2 or any other format that strikes your fancy.
Ok The swf file was something pulled from the internet, so if I try to open it in director or flash. it is locked preventing me from exporting it as a different file. I should have made that clear.....