MobileMe: Adding, renaming, or deleting folders on your iDisk
Summary
You can't rename or delete any of the default folders at the root level of the iDisk (the folders you see when you first open the iDisk).
Products Affected
MobileMe
The default folders are Backup, Documents, Library, Movies, Music, Pictures, Public, Sites, and Software. The default folders in this level are locked to make sure your uploaded images, movies, and documents are displayed correctly when you use them in an iCard, on your HomePage, or in your Public folder. Apple doesn't recommend creating any new files or folders at the root level of your iDisk.
Once you are inside any of the default folders, you can create or delete subfolders as you would in any other folder. Just keep in mind that some folders (such as Pictures and HomePage) may have files and folders in them that were put there by an application, which you should not remove or rename.