web server leaks a private IP address through its HTTP headers. how to fix?

I've already located this question on server fault:

Server Fault Question

But there is no answer. Does anyone have any advice on how to fix the issue? We're running 2003 Server R2 Ent, latest service pack is applied, IIS 6.0

Here's what the compliance company is saying:

Synopsis : This web server leaks a private IP address through its HTTP headers. Description : This may expose internal IP addresses that are usually hidden or masked behind a Network Address Translation (NAT) Firewall or proxy server. There is a known issue with Microsoft IIS 4.0 doing this in its default configuration. This may also affect other web servers, web applications, web proxies, load balancers and through a variety of misconfigurations related to redirection. See also : http://support.microsoft.com/support/kb/ articles/Q218/1/80.ASP

Any ideas?

Thanks