berdon, a member of zuneboards posted a method of using Zune as an external USB drive for your computer system. You can just add/delete/edit files. Here is the method how:

1. Apply External Hard Drive Patch / Registry Mod
2. Plug in your Zune
3. Turn on the software and press “Start Sync”
4. Quickly Begin transferring over a file from your computer to the Zune
5. Shutdown the Zune software while the transfer is still in progress
6. Transfer files through My Computer

This way Zune will stay open for new adding of files, until the it is unplugged. So now you can add files, delete files, create folders and do whatever you like.