I use the open-source Clonezilla at work for imaging machines. I keep images for each PC model on a network (NAS) drive and retrieve them using a Clonezilla Live CD at the workstation I want to restore. Any individual license details wouldn't take long after restoring a particular model from a stored image. I generally never have to enter a Windows license key, or re-activate the OS, after putting an image on another PC of the same model (mostly Dells).
Like the sound of Clonezilla! Is there a way of changing a Windows serial number afterwards i.e. if I use a serial to create my image but once I've added the image to another drive I want to change the serial? It's just that our I.T. department are somewhat paranoid about licensing and every now and then we have an audit of the computers checking licenses and I imagine they would have a heart attack if they found the same license in use on more than one machine.