If they're less than 15 mins, upload them to youtube, then download with realplayer (free). YT converts them to flv.
If they're longer, search free video converters. You could even do a free trial of camtasia. Import the vid and render the movie as flv. (I'm pretty sure that would work anyway). There is also the free version of camtasia, camstudio (I think they still have that anyway.
And there is also fiverr.