There's no way to disable HD detection. By default the HD's are detected but not mounted. They only get mounted if you click on the icon, then the default mount is read only. You have to deliberately remount read/write if you want to write to the HD.
If you don't want anyone to access (even read) the HD, the easiest way would be just to delete the Desktop icon. This will stop the unskilled user from accessing the HD but won't even slow down anyone who can work the command line. To control access for more skilled users, you would have to (as root) change the permissions on the HD to not allow anyone but root to even have read access to the drive then make sure your user does not have no-password sudo privilages.
I'm assuming you are running from CD. You would either have to redo this setup each boot or make a config floppy to do it all for you. Either way, your user could easily undo the setup & gain access to the HD's simply by rebooting the computer.