Customizing W3C Extended Logging (IIS 6.0)
If you selected the W3C Extended log file format for a Web or FTP site, you can customize the logged data. You can also limit unnecessary data and reduce the size of the log file by omitting unneeded fields.
You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /user:Administrative_AccountName "mmc %systemroot%\system32\inetsrv\iis.msc".
To customize W3C Extended logging