Downloading movies from TiVo Series 3 HD Recorder to Mac OS X
kmttg is a cross-platform Java program that does what you're looking for.  Personally I've used it on Windows without issue to copy shows off my Tivo onto my computer, do a batch convert of the video files, along with batch rename.  It's a very powerful and handy tool for any owner of a Tivo Series 3 or more recent Tivo.   It should run on modern Macs without issue.

You can grab it off Google Code here.  The Tivo Community forums have an extremely long-running thread about the tool here.