How to: Format your Zune's Hard Drive

Although I have not tried this, there have been several people confirming that this works. Please be advised the following steps will completely erase all your music, pictures, and videos. Do not attempt this if you still want anything on your Zune.

First, hold the back+down button to shut down.

During bootup...

Format EVERYTHING (Including firmware)
Hold the back+left_center to do a full format. (It will they go through several steps and ask you to connect your Zune to the PC and upload the latest firmware. You need to complete this for your Zune to run normal.

Format DATA ONLY
Hold back+right+center to erase your content (music/pictures/videos). Everything will run find but you will not find anything on your Zune.

That should do it, please leave some comments to let me know how it works out for you!