Banners leak very sensitive information to attackers wanting to penetrate your machine, such as version numbers and installed modules.
The web site www.nstalker.com offers a bunch of banner removal tools for the various servers.
IIS/PWS Banner Edit Tool
Changes the information server returns from an HTTP command, by editing the W3SVC.DLL in the Windows directory.
The tool can be downloaded from: http://www.nstalker.com/defense/IIS-Banner-Edit.zip