If you’re running Windows 7, you may periodically create a “System Image” which is essentially just a VHD backup of your system. When you invoke the task, you will be presented with a dialog box similar to the following, which shows the progress of the backup:
If you are scripting something, and want your script to proceed when the backup has completed, you can run this command line:
wbadmin.exe get status
This program will "block" (continue running) and report progress, as a percentage, until the backup has completed.