I've done the conversion and it's gone fairly well. I'm converting .mov to .flv, but my 480x360 movies turn into 320x240, even though I specified the medium 480x360 size. Odd and annoying.
Anyhow, yes it worked for me. The conversion just creates a .flv file in the same directory as the source video file. Have you looked in your directory to see if a new file is there?