function checkform() {
    // check form fields
    var ok = [];
	
	if((document.getElementById('ipod_quantity').value == '') && (document.getElementById('cell_quantity').value == '') )
	{
		ok.push('bags');
	}
	if (document.getElementById('terms').checked != true)
	{
		ok.push('terms');
	}
	
    if (document.getElementById('namefield').value == '') {
        ok.push('Name');
    }
    if (document.getElementById('emailfield').value == '') {
        ok.push('Email');
    }
    if (document.getElementById('address1field').value == '') {
        ok.push('Address 1');
    }
    if (document.getElementById('postcodefield').value == '') {
        ok.push('Postcode');
    }
    if (document.getElementById('cityfield').value == '') {
        ok.push('City');
    }

	
    if (ok.length > 0) {
        var message = 'You must fill out fields whose names are marked in bold: '+ok[0];
        for(i = 1; i < ok.length; i++) {
		
            message += ', '+ok[i];
			
        }

			if(ok[0] == 'bags')
			{
				message = 'You must enter either an iPod quantity or a Cell Phone quantity';
			}
			if(ok[0] == 'terms')
			{
				message = 'You must accept the Terms and Conditions first';
			}
   
        alert(message);
    } else {
        document.mainform.submit();
    }
}