If you dont have latest ajaxtoolkit installed on your visual studio 2008 download it from www.asp.net/ajax the binary file.
Paste it on a location on your system and the right click on the visual studio tookbox and choose items and browse to the dll file where you have stored. Press ok then all the controls will be loaded to your toolbox
Now add a standard textbox to the page and click on the top corner of the textbox and select add extender and select calendar from that, you are done.
when you click on the textbox the calendar will display and you can select the date
you can give readonly=true to the text box to avoid direct input from user
To set the UK date format, in the page directive give Culture="en-GB" UICulture="en-GB" and on the script manager give EnableScriptGlobalization="true"
your scrip looks like the following if you add an image on the right of text box and onclick of that will make the calendar display.
<asp:TextBox ID="TextBox13" runat="server" ReadOnly="true"></asp:TextBox>
<img src="images/calendar.gif" style="cursor:pointer" id="imgCalendar2" />
<cc1:CalendarExtender ID="TextBox13_CalendarExtender" runat="server" PopupButtonID="imgCalendar2"
Enabled="True" TargetControlID="TextBox13">
</cc1:CalendarExtender>
It can be even tried inside the edit item template of detailsview.