There is a script available on now, that does what you ask.
http://now.netapp.com/NOW/download/tools/disk_usage/
It is however a perl script, but you might be able to run it under perl for windows. Assuming there is a working implementation of the rsh command for windows, and if you could substitute something for the unix mail command. Lots of people use perl for windows, so it should be relatively easy to find a mail workaround. Not really sure about the rsh though.
The script also assumes that you are using user quotas. I got that impression from your message.
It would of course be easier to implement on a *NIX box if you have any.
Matt