In Windows Server 2008 and Windows Server 2008 R2, you can use the in-build tool Windows Server Backup to backup your Hyper-V virtual machines. However, there are some limitations:
1. You have to backup/restore all the virtual machines at the same time. It means you can't backup/restore individual virtual machines.
2. You have to backup the system drive and the drives contain virtual machine files. It means if you keep virtual machine in D:\ and E:\, you have to select C:\, D:\ and E:\ in the backup wizard.
3. You have to register the VSS Hyper-V Writer manually before the backup.
Now, in Windows Server 2012, there are some big changes.
1. You don't need to register the VSS Hyper-V Writer manually.
2. You can backup/restore individual virtual machines.
3. In the backup wizard, don't need to select the system partition and the partitions contain virtual machine files.
However, there are still some issues. You can't restore the virtual machine to original location on a different computer. The workaround is to rename this computer to the one which you performed the backup. But you can restore the virtual machines to another location in applications level, while this is not possible in Windows Server 2008 and Windows Server 2008 R2.