progressbar + background worker + reading a large XML file

I am trying to validate a large XML file against an XSD in C# code.  The file is 70MB in size.

I would like to have a progress bar so the windows app does not appear to hang.

How can I implement the background worker and progress bar?  The user can select any XML file and XSD, so the nodes will be completely different - so I'm not sure how to count all the nodes to use as progress when I won't know the node names.

private void button3_Click(object sender, EventArgs e)
        {
            // create object for the XSD file that will be used
            // for validating the XML file. Use the Connection
            // Manager to get the path from the XSD file.
            XmlReaderSettings xmlrs = new XmlReaderSettings();
            xmlrs.ValidationType = ValidationType.Schema;
            xmlrs.Schemas.Add(null, txtXSDPath.Text);
            xmlrs.ValidationEventHandler += new ValidationEventHandler(ValidationCallBack);
            xmlrs.Schemas.Compile();

            XmlDocument doc = new XmlDocument();
            doc.Load(txtXMLPath.Text);
            long filelength = doc.OuterXml.Length;

            


            // Try reading the XML file using the XSD. Use the
            // Connection Manager to get the path from the XML file
            try
            {
                XmlReader xmlr = XmlReader.Create(txtXMLPath.Text, xmlrs);


                while (xmlr.Read())
                {
                }
                // The XML file was succesfully read.
                //Dts.TaskResult = (int)ScriptResults.Success;
                if (errorcount == 0)
                {
                    txtValidated.Text += "The XML is valid";
                }
            }
            catch (Exception ex)
            {
                // Validation failed
                txtValidated.Text +=  Environment.NewLine + ex.Message + Environment.NewLine + "--------------------------------------";
            }
        }


        //Display any warnings or errors.
        private  void ValidationCallBack(object sender, ValidationEventArgs args)
        {
            if (args.Severity == XmlSeverityType.Warning)
                txtValidated.Text += (Environment.NewLine + "\tWarning: Matching schema not found.  No validation occurred." + args.Message.ToString() + Environment.NewLine + "--------------------------------------");
            else
                txtValidated.Text += (Environment.NewLine + "\tValidation error: " + args.Message + Environment.NewLine + "--------------------------------------");
            errorcount++;
        }