You need ESX hosts connected to SAN storage and a Windows 2003 server also connected to those SAN LUNs. On the Windows server (this is the Consolidated Backup Proxy) you install the VCB framework and an agent of your backup agent. When doing a backup of a VM the backup software runs the pre-script of the VCB framework to do a snapshot of the VM, then makes a backup of those files provided by the snapshot, and last runs the post-script of the VCB framework to remove the snapshot.
See http://www.vmware.com/pdf/vi3_301_201_vm_backup.pdf p23 for more information
