Forçar saída xml

Response.Clear();
Response.ClearContent();
Response.ClearHeaders();
Response.ContentType = "text/xml";
Response.Write("seu xml aqui");
Response.End();

Forçar download de arquivo

Response.Clear();
Response.AddHeader("content-disposition", "attachment; filename=" + "MyMusic.mp3");
Response.WriteFile("~/Downloads/MyMusic.mp3");
Response.ContentType = "";
Response.End();