mbox mail notifier

[Dan Christensen]

I download my e-mail with a program like fetchmail, with the messages
stored in an mbox folder.  I'd like a menu bar icon that shows the
number of unread messages.  Basically, it should run the following
command once a minute and display the output in the menu bar:

  grep '^From ' /path/to/mbox/folder | wc -l

I've searched and can't seem to find a notifier that handles plain
mbox files.  Does anyone know of one?  Barring that, can someone
explain how to write the necessary code to create a menu item?
I'm quite familiar with C and python, and am comfortable in several
other languages as well, but am new to the Mac.

Dan