We have the same problem and we went to the same people I posted about yesterday called "trouble with user deleting and moving files". Niwot Networks (
http://niwotnetworks.com/) They created a program which we keep on our project server that scans the drive for folders that have had no activity for 4 months (you can set it to any time you want) if it finds any, it will move the folder to an "Inactive Projects" folder on another server that it set to read-only for everyone but me. Once the folder is moved an email it sent to me (and few other people) to notify us that the project has moved. We can then decide if we want to burn it off to disk etc. No one but a select few know that location and with the the You Got Files program I know if someone copies it back to the project file server. We've only had this system going for a short time but so far it's working. It's simple and it makes my life much easier!
~Cynthia