[Joe]

Windows = Makes the BEST workstation OS available for functionality and productivity in no small part by the proliferation of Office as the king of productivity packages. And makes a solid simple to use file server and terminal service OS. Also Windows provides a director to base authentication on and many authentication based services. More groupware oriented.

Linux/BSD = the best OS for areas where the Server must be hardened and protect itself from outside attacks. Also the best for console-less services such as MySQL/Apache/etc.. Makes a great web server, and solid "service" server for higher end environments. More service and service support oriented.