It depends on what type of storage you use.
If the VM files reside on shared storage (SAN, NFS, etc.) that both ESX servers can access, you don't need to copy anything. Just shut down the VM on the first server, register it on the second, and start the VM on the second. You can register using the VI client or the command line (vmware-cmd -s register path-to-vmx-file.vmx).
If the servers don't share storage, you have to copy the files in some way, and that would mean FTP, SFTP, or other methods. How to do this depends on what ports you want to open up on the ESX firewalls, and which services you want to run. After the copy, you would register the VM as above.
