The IIS log files that are stored in %SystemRoot%\system32\Logfiles\<server_name>. They are formatted differently based on the logging type that is configured for the site.
For definitions of IIS logging types and the fields of each log file, see the section titled "Logging Properties Reference" in the IIS administration guide that is included with IIS. Or, see the topic Logging Properties Reference on the Microsoft TechNet Web site or see Analyzing Log Files.
Client: Requires Windows XP Professional, Windows 2000 Professional, or Windows NT Workstation 4.0.
Server: Requires Windows Server 2003, Windows 2000 Server, or Windows NT Server 4.0.