I guess you have a problem with your httpd.conf configuration,
you can modify the headers apache sends with the Header directive.
http://httpd.apache.org/docs/2.0/mod/mod_headers.html#header

In order to debug the headers, you could telnet to your apache server:
telnet localhost 80

Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
[download]

GET /now.xml
This way you'll get the full response of apache.

I use firefox with firebug (http://www.getfirebug.com/)
Within firebug you can debug the headers, too.
Michael