Why don't you mention the OS, for real now?
If Windirstat isn't what you're looking for, although I highly doubt there's anything "better" out there, try
http://w3.win.tue.nl/nl/onderzoek/on...n/sequoiaview/
You can create quotas for every drive/user, limit certain file types and whatnot all with windows built in tools, depending on the version you're using ...