How can I Show an XmlDocument.innerXml Indented?

Hi guys... I have this problem... I'm using an XmlDocument.innerXml in a message box... and I want the text indented inside the message box... I'm using this code inside a Function:

            private string convertXmlToString()
            {
            XmlDocument document = new XmlDocument();
            document.Load(@"C:\books.xml");
            string resp = Convert.ToString(MessageBox.Show(document.InnerXml, "Books"));
            return resp;        
            }