Setting charset in IIS headers

Referencing this web page:
<http://www.w3.org/International/O-HTTP-charset.html>
http://www.w3.org/International/O-HTTP-charset.html
 
It describes a procedure for setting a charset for localized pages:
 
*	For IIS 4 and 5, in Internet Services Manager, right-click "Default
Web Site" (or the site you want to configure) and go to "Properties" =>
"HTTP Headers" => "File Types..." => "New Type...". Put in the extension you
want to map, separately for each extension; IIS users will probably want to
map .htm, .html, .asp,... Then, for Content type, add
"text/html;charset=iso-8859-1" (without the quotes; substitute your desired
charset for iso-8859-1; do not leave any spaces anywhere because IIS ignores
all text after spaces). 
 
I am unable to make this work. For an asp, the web server always returns
"Content-Type: text/html", even when I define it to be something else. I
created a new extension .xyz, and managed to have it set that correctly, but
no matter what I do for "asp" it ends up as "text/html". Just curious if any
of you can help me make this work.
 
Thank you,
Dave Ringoen
Alventive, Inc.