var today = new Date();
var buffer = Date.parse(today);
var number = 4; //number of days to add
number = number*24*60*60*1000;
var newDate = new Date(buffer + number);
var frm = document.forms.frmARNQuickSearch;
frm.selMonth.selectedIndex = newDate.getMonth();
frm.selDay.selectedIndex = newDate.getDate() - 1;