HttpHandler and XML files

I would like to intercept any request made to the server for XML files. I thought that it might be possible with an HttpHandler. It's coded and it works... on localhost only (?!?!).

So, why is it working on localhost only? Here is my web.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <httpHandlers>
      <add verb="*" path="*.xml" type="FooBar.XmlHandler, FooBar" />
    </httpHandlers>
  </system.web>
</configuration>

Here is my C# :

namespace FooBar
{
    public class XmlHandler : IHttpHandler
    {
        public bool IsReusable
        {
            get { return false; }
        }

        public void ProcessRequest(HttpContext context)
        {
            HttpResponse Response = context.Response;
            Response.Write(xmlString);
        }
    }
}

As you might have seen, I'm writing the xmlString directly in the response, it's only temporary because I'm still wondering how I could give the filename instead (that's the second question ;) )

What is supposed to be written in the response is only the xml filename that will be retrieved by a flash app.

Thanks

Details :
Using IIS 6.0 on Windows Server 2003.

Edit :
When calling the page from another computer it looks like it's not getting to the HttpHandler. However, the mapping for IIS have been done correctly.