is there shared storage between the two clusters? If so, make a note of the ESX Host the vCenter VM is running on as well as what datastore it's registered on. From there login to the ESX Host and shutdown the vCenter VM, then remove it from inventory. Login to the destination ESX host, find the datastore in question, browse the datastore and right click on the vmx file and "add to inventory"
If you don't have shared storage, you can use VMware Converter to move the guest. Once the new guest is up and running and all is good, destroy the "old" one.
