I came accross a method for seeing who is listening to your iTunes Music Shares on a mac or a windows box.
netstat -a | grep yourcomp.domain.com.daap
netstat -a | grep computername:3689
On a windows box you will need to install grep which is part of UnixUtils for win32. Of course I have only tested the mac version =)
The computers lisetning to your music (or atleast connected to your share) will be under Foreign Address