The link below will give you details on each version. Backup Exec needs a licensed ESX or ESXi server because it's using the vStorage API as you see this is available in the Essentials version
http://www.vmware.com/products/vsphere/buy/editions_comparison.htmlIt's still @$500 but says price will go up June 15 so you may still have this option
http://store.vmware.com/store/vmware/en_US/DisplayProductDetailsPage/productID.126843700If you bought the Backup Exec with vmware agent you may have paid a lot more than you needed. A copy of vRanger or Veeam Backup would have been much cheaper and given you more options. How much did the vmware agent cost you?