Restoring drive

Hi can anyone help, i have booted my mac from an external drive and now i want to use carbon copy cloner to restore my main hard drive back to leopard, i have set up the the source disk as the external bootable drive and the destination disk as the internal main hard drive, there is a warning coming up that says" The target volume already has Mac OS X installed. Copying a different version of Mac OS X to this volume may render it unbootable." is it ok to carry on