rxml output to file not working in IE

I want to use Builder (.rxml template) to generate xml but instead of having it display in the browser I want it to offer a file download.

I am using the following code in my controller:

respond_to do |format|       format.xml { render :layout => false, :content_type => "application/octet_stream"} end

This works as desired in Firefox, but in IE (both 6