5 Update 6 without upgrading VMware Update Manager( VUM) and VMware Converter, the ESX hosts in Inventory are disconnected. But why don' t you download an evaluation copy of VMware vCenter Server 4. It has more features than VMware VirtualCenter 2. 5 and it works perfectly well with ESX 3. For information about which ESX server versions are supported by VMware vCenter Server 4.