Use SharePoint controls in Custom page - Calendar Controls

Put the code in markup file(.aspx or .ascx), on the starting of the markup.

<%@ Assembly Name="Microsoft.SharePoint,Version=12.0.0.0, Culture=neutral,PublicKeyToken=71e9bce111e9429c" %>
<%@ Register TagPrefix="MySPUserControl" Namespace="Microsoft.SharePoint.WebControls" Assembly="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c" %>


Put the code in body of markup file.
<MySPUserControl:DateTimeControl ID="txtEstimatedCompletionDate" runat="server" DateOnly ="true" IsRequiredField="true" ErrorMessage="*" />

CAML Compatible Time String.

SPUtility.CreateISO8601DateTimeFromSystemDateTime

Publishing Feature Activation error after SharePoint 2007 to 2010 migration

http://www.mssharepointtips.com/tip.asp?id=1018