<script type="text/javascript">
function Watermark()
{
var txt=document.getElementById("TextBox1").value;
if(txt=="Enter User Name")
{
document.getElementById("TextBox1").value="";
}
}
function RemoveWatermark()
{
var txt=document.getElementById("TextBox1").value;
if(txt=="")
{
document.getElementById("TextBox1").value="Enter User Name";
}
}
</script>
<div>
<asp:TextBox ID="TextBox1" Text="Enter User Name" onblur="return RemoveWatermark()" onfocus="return Watermark()" runat="server"></asp:TextBox>
</div>