I don't see any good reason to use Windows for servers unless you want to use programs which work with Windows only.
Linux is more secure, more reliable and free (well, okay, you have to know how it works...).
Who the hell thinks that using ANY Windows Server OS's is a good idea? Not only are you limited with how many licenses you can have, but Windows is also unstable compared to Linux Red Hat, or any other Ubuntu distributions for server machines, and that on top of that Windows 2003 server has a limit to how many IP addresses you can hand out per license! What the hell!
I don't see any good reason to use Windows for servers unless you want to use programs which work with Windows only.
Active Directory - Setup 'global' users, which are accessable from every windows-system in the server-network. It's typical used in schools..
(Actually I don't know if there is software for linux, which does the same job, too)
It's outdated, if you're going to use a Window IIS use Windows 2008 R2.
@ DC: Well no, exploits come out for the operating system with the most users.
On the pc, there are more viruses, and on serverside, there are more people trying to hack linux and succeeding.
However, if there are software that can run on linux then you really don't need windows, unless you're doing something really special.