i found a cool tool can help u,but its not freeware.u can free trail--Flash Video MX Pro ,it can converts AVI to SWF/FLV, DVD to SWF/FLV, MOV to SWF/FLV, WMV to SWF/FLV, MP4 to SWF/FLV, 3GP to SWF/FLV, MPEG to SWF/FLV, etc.
I second the use of ffmpegX. I've used it before to convert some movies I've made into FLV files. All you need to play them is an embedded Flash movie player (which is in SWF format) like the JW FLV Media Player.