var firstErrorField = '';

function checkForm(form) {
	var alertText = '';
	firstErrorField = '';
	
	if (!form.firstName.value) {
		alertText += "Please enter your first name.\n";
		checkFirstErrorField('firstName');
	}
	if (!form.lastName.value) {
		alertText += "Please enter your last name.\n";
		checkFirstErrorField('lastName');
	}
	if (!form.email.value) {
		alertText += "Please enter your email address.\n";
		checkFirstErrorField('email');
	}
	else {
		if (!(emailCheck(form.email.value))) {
			alertText += "Please enter a valid email address.\n";
			checkFirstErrorField('email');
		}
	}
	if (!form.phone.value) {
		alertText += "Please enter a phone number where we can contact you.\n";
		checkFirstErrorField('phone');
	}

	if (!form.address.value) {
		alertText += "Please enter your billing address.\n";
		checkFirstErrorField('address');
	}	
	if (!form.town.value) {
		alertText += "Please enter your town and state of residence.\n";
		checkFirstErrorField('town');
	}
	if (!form.zip.value) {
		alertText += "Please enter your zipcode.\n";
		checkFirstErrorField('zip');
	}
	if (!form.startDate.value) {
		alertText += "Please enter your ad start date.\n";
		checkFirstErrorField('startDate');
	}
	if (!form.adPhone.value) {
		alertText += "Please enter the phone number for the ad.\n";
		checkFirstErrorField('adPhone');
	}	
	if (!form.adText.value) {
		alertText += "Please enter your classified ad text.\n";
		checkFirstErrorField('adText');
	}
	
	if (!form.captchaCode.value) {
		alertText += "To help prevent spam posts, please type the characters you see in the graphic.";
		checkFirstErrorField('captchaCode');
	}
	else if (form.captchaCode.value != captcha) {
		alertText += "The security code you typed in is incorrect.";
		checkFirstErrorField('captchaCode');
	}
	
	if (alertText != '') {
		alert(alertText);
		form[firstErrorField].focus();
		form[firstErrorField].select();
		return false;
	}
	else {
		form.submit();
	}
}