How can I fix Transaction with Page Lock Ploblem ?

Question

My Application has ploblem while one of client save Order Document. Another client cannot select data from Order table until saving process is complete. I develop C# window application with Microsoft SQL Server 2005 sp3. I used Transaction and Isolation=ReadUncommit to save Order Document. My Application has 3 table is OrderHd, OrderLine and OrderSerial. Record of OrderSerial per 1 Order Document about 1,000-5,000 record

  //My Simulate Saving Process
 private void btnSave_Click(object sender, System.EventArgs e)
 {

  string mstrConnStr = "Data Source=serverzx; Initial Catalog=Test;User ID=sa;Password=x2y2;";
  System.Data.SqlClient.SqlConnection conn = new SqlConnection(mstrConnStr);
  System.Data.SqlClient.SqlCommand cmd1 = new SqlCommand("Insert Into OrderHd (OrderID , Code,Name) values (@Para0,@Para1,@Para2)",conn);
  System.Data.SqlClient.SqlCommand cmd2 = new SqlCommand("Insert Into OrderLine (OrderLineID , OrderID,Detail) values (@Para0,@Para1,@Para2)",conn);

  System.Data.SqlClient.SqlTransaction tr = null;

  try
  {
   conn.Open();

   cmd1.Parameters.Clear();

   tr = conn.BeginTransaction(IsolationLevel.ReadUncommitted);
   //tr = conn.BeginTransaction();

   string strCode = DateTime.Now.ToString("yyyyMMdd : HHmmss");
   string strHead = Guid.NewGuid().ToString();

   cmd1.Transaction=tr;
   cmd2.Transaction=tr;

   cmd1.Parameters.Add("@Para0",strHead);
   cmd1.Parameters.Add("@Para1",strCode);
   cmd1.Parameters.Add("@Para2","Name "+strCode);
   cmd1.ExecuteNonQuery();

   for (int i=0;i<5000;i++)
   {
    string strItem = Guid.NewGuid().ToString();
    cmd2.Parameters.Clear();
    cmd2.Parameters.Add("@Para0",strItem);
    cmd2.Parameters.Add("@Para1",strHead);
    cmd2.Parameters.Add("@Para2","Detail "+i.ToString());
    cmd2.ExecuteNonQuery();
    System.Threading.Thread.Sleep(10);
   }
   tr.Commit();
  }
  catch (Exception ex)
  {
   tr.Rollback();
   MessageBox.Show(ex.Message);
  }
  finally
  {
   conn.Close();
  }
 }