Javascript "watermarks" for textboxes

I would like to know how to put text in a textbox when the page loads. Example: If I have a page with labels and inputs, from that i would have two textboxes named "Start Date" and "End Date". When the page loads I want the the textbox to load with "dd/mm/yyyy" written inside, so I won't have to put a label for that outside. But when the user clicks inside textbox it should disppear. How do I do this?

Javascript "watermarks" for textboxes can be done as shown in the following example

<input name="txtDate" on-focus="if (this.value=='dd/mm/yyyy') this.value = ''" type="text" value="dd/mm/yyyy">