I haven't tried it with .dv files, but I have used with other Video Files.
But as far as I understand, you should be able to open the .dv file in Quicktime.
From Quicktime you should be able to Export to an audio-only file type.
This most likely requires Quicktime Pro.
Another Method would be to use some Audio Recording Software like Audacity to record your system sound, and just play the .dv file, recording the sound as it plays.
-- Issues with this method is that it would take longer as you have to play the file back, and any other sounds that your system makes like alerts would also be recorded...
Hope this helps.