VMware offers a (Windows only) program called Virtual Client to connect to either ESX Server directly or to a (Windows only) VirtualCenter server that aggregates connections to multiple installations of ESX Server. In Virtual Client, there is a “Right click to clone” operation much like there is in VMware Workstation. Unfortunately, this is not available in Virtual Client unless connected to a VirtualCenter Server. Argh. Both components can be installed on the same Windows box, so it’s not a huge obstacle, but it’s another hundred-something megabytes to download. Anyways, here is a set of instructions that I have used to successfully clone a VM on ESX Server without having a VirtualCenter server.