You can set up accounts for users of your wireless network to control how a user shares USB hard disks connected to your base station. If you’re using a Time Capsule, you can set up accounts for users of the internal AirPort disk.
Open AirPort Utility, located in the Utilities folder in the Applications folder on a computer using Mac OS X, and in Start > All Programs > AirPort on a Windows computer.
Select the device you’re setting up, and then click Manual Setup. Enter the password if necessary.
Click Disks in the toolbar, and then click File Sharing.
Choose "With accounts" from the Secure Shared Disks pop-up menu, and then click Configure Accounts.
Click Add (+), enter the user name, and then give the user a password.
Choose Read and Write, Read Only, or Not Allowed from the File Sharing Access pop-up menu, depending the access privileges you want to assign for this user.