Validation of two Calendar controls

Hello there,
I would, kindly, ask for help.
I have 2 Calendar control dateFrom and dateTo and I want to be able to notify user when he choses dateFrom which is later than dateTo.
Here's what I have, atm:
Logs.aspx:
<asp:Calendar ID="dateFrom" runat="server" OnSelectionChanged="dateFrom_SelectionChanged"> </asp:Calendar> <asp:Calendar ID="dateTo" runat="server" OnSelectionChanged="dateTo_SelectionChanged"> </asp:Calendar> <asp:TextBox ID="TextBoxdateFrom" runat="server" ></asp:TextBox> <asp:TextBox ID="TextBoxdateTo" runat="server" ></asp:TextBox> <asp:CompareValidator ID="CompareValidator1" runat="server" ControlToValidate="TextBoxdateFrom" CotrolToCompare="TextBoxdateTo" Op ...