function isNumeric(s)
{
   return !(/[^\d\.]/.test(s));
}

function calcPmt(form) 
{
	var errmsg = '';
	var taxes, ins, int, pmt;
	
	if(form.loanAmt.value == '')
		errmsg += 'Please enter the Loan Amount.\n';
	else if(!isNumeric(form.loanAmt.value))
		errmsg += 'Loan Amount must have numbers only.\n';
	if(form.int.value == '')
		errmsg += 'Please the Interest Rate.\n';
	if(!isNumeric(form.int.value))
		errmsg += 'Interest Rate must have numbers only.\n';
	if(!isNumeric(form.taxes.value))
		errmsg += 'Taxes must have numbers only.\n';
	if(!isNumeric(form.ins.value))
		errmsg += 'Insurance must have numbers only.\n';
	if(errmsg == '')
	{
		taxes = form.taxes.value/12;
		ins = form.ins.value/12;
		
		if(form.io.value == 'Yes')
		{
			int = form.int.value * .01 / 12;
			pmt = (form.loanAmt.value * int) + taxes + ins;
			form.pmt.value = '$' + Math.round(pmt*100)/100;
		}
		else
		{
			per = form.yrs.value * -12;
			int = form.int.value * .01 / 12;
			loan = form.loanAmt.value;
			form.pmt.value =  (loan * int) / (1 - (1 + int)^per);
			
			pmt = (loan * int) / (1 - Math.pow(1 + int, per));
			pmt = pmt + ins + taxes;
			form.pmt.value = '$' + Math.round(pmt*100)/100;
		}
	}
	else
		alert(errmsg);
}