function selectAll(selectBox,id) { 
	var value = document.getElementById(selectBox).checked; 
	var table = document.getElementById(id + 'table'); 
	var inputs = table.getElementsByTagName("input"); 
	for (var i=0,len=inputs.length; i<len; i++) { 
		inputs[i].checked = value;
    } 
}
function checkform(form) {
	var dm_listings = 0;
	var dm_listings_table = document.getElementById('dm_table');
	var dm_listings_inputs = dm_listings_table.getElementsByTagName("input");
	for (var i=0,len=dm_listings_inputs.length; i<len; i++) { 
		if (dm_listings_inputs[i].checked) {
			dm_listings++;
		}
    }
	var cr_listings = 0;
	var cr_listings_table = document.getElementById('cr_table');
	var cr_listings_inputs = cr_listings_table.getElementsByTagName("input");
	for (var i=0,len=cr_listings_inputs.length; i<len; i++) { 
		if (cr_listings_inputs[i].checked) {
			cr_listings++;
		}
    }
	var ag_listings = 0;
	var ag_listings_table = document.getElementById('ag_table');
	var ag_listings_inputs = ag_listings_table.getElementsByTagName("input");
	for (var i=0,len=ag_listings_inputs.length; i<len; i++) { 
		if (ag_listings_inputs[i].checked) {
			ag_listings++;
		}
    }
	if (dm_listings == 0 && cr_listings == 0 && ag_listings == 0) {
		alert("You must select at least one box.");
		return false;
	} else {
		return true;
	}
}