You can cal the Date() function on onClick event and display the old date in the first field you should disable the first field .i think this is what u want ......just see the code below
<script type="text/javascript">
var mm = ['January','February','March','April','May','June','July','August','September','October','November','December']
function setday(obj){
this.y = obj.getFullYear();
this.m = obj.getMonth();
this.d = obj.getDate();
}
function ShowDate(){
var today = new Date();
var dd = new setday(today);
var h = today.getHours();
var tomor = new Date(dd.y,dd.m,dd.d-10);
var tt = new setday(tomor);
var theDay =(h>=14)?tt:dd;
var real=theDay.d+' '+mm[theDay.m]+' '+theDay.y;
document.menuform.name2.value=real;
alert(real)
}
</script>
Unsolved 
