@RodAtWork: There are a lot of different ways to do so. Windows 7 and 8 have the option to create a system image built into the backup tools. Basically this creates a copy of your entire system drive (and optionally additional drives) that can be restored to instantly recover your system to a previous state.

Note that this isn't really the best option for installing multiple PCs. If the PCs are not all identical you may have driver problems, and even if they are the system image includes the product key and activation information (I think you can change that, but it's a bit of a hassle).

For your purposes, something like the Windows Automated Installation Kit is probably better. This allows you to revert a system to a state where it will re-run the OOBE wizard on next boot so you can add a new product key and perform hardware detection etc. (and provide answers for many questions beforehand so the installation runs unattended). You can create an image in wim format (which is what the Windows installation DVDs use) and install it just like you install Windows from scratch, only with all the extra stuff you added to the image included. If you have a Windows Server in your network, there are also ways to automatically deploy these images.