When using the DatePickerControl in a custom SharePoint page, I found there's an issue with the rendering of the calendar when you click on the 
The calendar renders like there are no styles - because there aren't. For some reason, there is no stylesheet reference to the datepicker stylesheet when you use the control for your own use, but the control works fine when rendered dynamically in a list edit form.
To fix the problem, drop the following line of code into %programfiles%\common files\microsoft shared\web server extensions\12\templates\layouts\iframe.aspx
<link rel="stylesheet" type="text/css"href="/_layouts/1033/styles/datepicker.css"/>
Put it right below the <HEAD> tag at the top, and the calendar should render correctly from now on..