Ms Office Offline Installer [best] -

Hard drives crash. Operating systems need to be reinstalled. When the inevitable happens, the last thing you want to do is wait for 3GB of data to download from a slow server. With the offline installer saved to a USB drive or an external hard drive, you can restore your productivity suite in minutes, regardless of your bandwidth speed.

This is the professional method. You download a small tool that creates a custom offline installer for you. ms office offline installer