This is 1 of the most commonly asked question & since the release of Windows 2000, IIS is no longer available for download as it is part of the OS.
IIS 4 was the last version of IIS that was available for download. Since the advent of Windows 2000, IIS has been part of the OS & is NOT available for download.
OS Version – IIS Version
Windows 2000 – IIS 5
WindowsXP Pro – IIS 5.1
Windows Server 2003 – IIS 6