Switching to a new version of Windows is virtually a nightmare if you have to manage more than 100 PC. This is why I value a lot a tool like Microsoft Deployment Toolkit 2010 Beta 2. A tool that can be downloaded here.

MDT 2010 is the next version of Microsoft Deployment Toolkit, a Solution Accelerator for operating system and application deployment. New features such as flexible driver management, optimized user interface workflow, and Windows PowerShell can simplify deployment and make your job easier. MDT 2010 will support deployment of Windows 7 and Windows Server 2008 R2 in addition to deployment of Windows Vista®, Windows Server 2008, Windows Server 2003, and Windows XP