How does the vmware backup works , I have a vm still running on snapshot and i cannot create new snapshot , in that case will it work
No. No snapshots must exist for BacckupExec to do it's backups of the VMDK's.
BackupExec integrates with VMware via vCenter communication. There is a feature within VMware called vStorage API that backup vendors integrate to.
BackupExec tells vCenter it wants to backup a certain host. It initiates a snapshot, and that snapshot is mounted by BackupExec and moved to your eventual target (e.g. Tape or disk)
Of course you need to be licenced with the Vmware option from backupExec, as well as be licensed with the right version of Vmware that includes the vStorage API's. The free version of ESXi does not include it.
There is an online portal, save yourself the long hold times. Create ticket online, then call in with ticket # in hand :-) http://mysupport.symantec.com "We backup data to restore, we don't backup data just to back it up."