php > XML output in IE: no display

Has anyone figured out how to trick IE into displaying an XML file that is produced by a PHP script (script.php) properly? What happens usually is that you send the mime 'text/xml', but IE still sees content as php because the script is called php. Also adding <Content-disposition: filename="some.xml"> to the header does not help and is boldly ignored by IE. Nice detail: if the url is called using Netscape, Netscape will save the file out to the disk, give it the suffix .xml and call IE which then will display content perfectly. Any hints are greatly appreciated. greets, patrick./