You should use compareValidator to compare From date and To Date
<asp:CompareValidator ID="Comparevalidator1" runat="server" ErrorMessage="To date must be greater than From date"
Operator="GreaterThan" ControlToValidate="txtToDate" ControlToCompare="txtFromDate" Type="date" />
For comparison with today you can use another compareValidor as
<asp:comparevalidator runat="server" Id="Comparevalidator2"
errormessage="To date must be less than today"
controltovalidate="txtToDate" type="Date" Operator="LessThan"
ValueToCompare="<%= DateTime.Today.ToShortDateString() %>" />
In the same way for From date
<asp:comparevalidator runat="server" Id="Comparevalidator3"
errormessage="From Date must be greater than today"
controltovalidate="txtFromDate" type="Date" Operator="GreaterThan"
ValueToCompare="<%= DateTime.Today.ToShortDateString() %>" />