Usefull wbadmin commands

wbadmin [] [-backupTarget:{VolumeName NetworkSharePath}][-machine:BackupMachineName]

List the disks that are currently online for the local computer
WBADMIN GET DISKS

Backup c: drive
WBADMIN START BACKUP -backupTarget:e: -include:c: -quiet

Create a backup of the system state
WBADMIN START SYSTEMSTATEBACKUP -backupTarget:e: -quiet

e:\WindowsImageBackup\[machinename]
It is possible to backup multiple machines using the same external drive

In the case of Hyper-V Virtual Machines you have to shutdown the VM to switch external drives.
The limiting factor is that both the source and target drives have to be locally attached.
In the case of SBS 2008 Premium where you use 2 VMs you would want 2 external usb drives. If you have a larger number of VMs that require backup an alternative solution is desirable.

See blog about setting up pass through drives for use with VMs.

Used in conjunction with the Windows Server Backup GUI it is possible to restore backups for this or other machines. You can also backup the machine from the GUI.

See blog about setting up Windows Server Backup on Windows 2008.

Running from a batch file & scheduling
Create file c:\backserver.cmd with following contents
wbadmin start backup -backupTarget:e: -allCritical -quiet

open command prompt and enter the following to schedule the backup
at 21:00 /every:M,T,W,Th,F c:\backserver.cmd

These commands will backup the system drive, including system state, at 9pm every week day