Enabling/Disabling VALIDATION according to a condition!

Hi guys,
Ok, what i'm trying to do is this:
- I have this check list:
<asp:CheckBoxList ID="itemsCheckList" runat="server">                        
     <asp:ListItem Value="001">Item 1</asp:ListItem>
     <asp:ListItem Value="002">Item 2</asp:ListItem>                                         
</asp:CheckBoxList>


- And i have another 2 Check lists with VALIDATION as follows:
<asp:CheckBoxList ID="Checklist1" runat="server">        &nb ...