Numbers Only in textbox

<SCRIPT language=Javascript>

      <!--

      function isNumberKey(evt)

      {

         var charCode = (evt.which) ? evt.which : event.keyCode

         if (charCode > 31 && (charCode < 48 || charCode > 57))

            return false;

         return true;

      }

      //-->

   </SCRIPT>

 <asp:TextBox ID="txtname" runat="server" Width="241px" BorderColor="#CCCCCC"
                                    BorderStyle="Solid" BorderWidth="1px" CssClass="txtradius" onkeypress="return isNumberKey(event)"></asp:TextBox>