You have to boot into the WinRE (Recovery) environment (boot to Recovery CD or Install DVD). There is an option there to restore a system image. As you can imagine, the drive being restored may be new so you have to start the image restore from outside of Windows.
You can get into the WinRE using the F8 key during boot also, but I have not tried a restore from there. Go to Repair Your Computer and select the Restore from image option.