You can try to handle the key down event and discard any keys you
want. Look at this code. Create a form and add datetimepicker control.
HTH.

Alcides Schulz.(http://alsql.blogspot.com).

   public partial class TestDatePicker : Form
   {
       public TestDatePicker()
       {
           InitializeComponent();
           dateTimePicker1.KeyDown += new
KeyEventHandler(event_KeyDown);
       }

       private void event_KeyDown(object sender,
System.Windows.Forms.KeyEventArgs e)
       {
           Console.WriteLine("KeyDown=" + e.KeyCode.ToString());
           if (e.KeyCode.ToString() == "Down" || e.KeyCode.ToString()
== "Up")
           {
               e.SuppressKeyPress = true;
               return;
           }

       }
   }