Scripting

GPO cannot solve everything.  MDT is the best way to go or if you have a management server that can create an image and push it out to target pcs.  Take a look at this link http://technet.microsoft.com/en-us/video/microsoft-deployment-toolkit-mdt-demo-using-mdt-to-quickly-and-efficiently-deploy-windows-7-across-your-organization.aspx.  I feel as if GPO is only good enough for pushing tasks, simple software, and rules to end users.  For bigger projects such as operating systems, you will need to use a more reliable tool.  You have to consider many variables when doing a OS upgrade for all your pcs.  The current version its running, programs, services, printers.  And even to if all your pcs can handle a 64 bit archetecture.  with MDT you can push out the image to a sinle or multiple end user pcs.