According to this post, there\'s a separate DatePicker control in .net 4. I\'ve tried it, and I don\'t see a good way to also let it select the time of the day.
Extended WPF Toolkit sports a nice DateTimePicker with time of day.
There is also an article over on CP where someone created a control that works like the Winforms one... A WPF DateTimePicker That Works Like the One in Winforms