Best practices duplicating a machine

I am in the higher education industry and we have several computer labs all with the same exact PC configurations. (Windows XP with the same software and permissions) Every semester or two I want to reload all the computers in the labs with the original image as when I first loaded the machines, keeping the original software and user permissions. I want to be able to do a whole computer lab at once. Does anyone have any past success stories they would like to share with me? Reloading each machine with the same software takes entirely too long. Thanks in advance.