validate with validation control to dropdown list

Hi
i have a dropdownlist and validate  with validation control if no item selected
 <asp:DropDownList ID="DropDownList1" runat="server" Width="130">
                <asp:ListItem Text="computers" Value="0"></asp:ListItem>
                <asp:ListItem Text="vechiles" Value="1"></asp:ListItem>
             
            
            </asp:DropDownList>
...