To clone existing VM on vmware esxi  simply browse to the datastore:

• Click on the host > Configuration tab
• Select Hardware > Storage to display the datastores
• Right-click on the datastore with the VM you want to clone > Browse Datastore
• Create a new folder in the store
• Right click on the VM folder and select Copy (must be done in the right pane of the Datastore Browser)
• Paste the VM to a new sub folder (otherwise the VM will overwrite itself)
• Once copied, rename and move the folder if desired
• Select the .vmx file within the cloned VM and select ‘Add to Inventory’

thanx to http://serverfault.com/questions/16320/is-there-a-way-to-clone-an-existing-vm-on-an-esxi-server-without-having-to-re-im