Install Windows for iMac (21.5-inch, Late 2012)

This will be a very hot question for 2013. How to install Windows for iMac (21.5-inch, Late 2012)?

With the use of no disc drive being the latest in Apple technology, it makes it difficult to 'pop-in' a disk and install. How can this be done? Can you provide a link to seamlessly download this from Microsoft?

Users have loved the iPhones and are now switching to iMac's. However, much of the software purchased is sitting on Windows based computers.