function IsEmpty(aTextField) {
	if ((aTextField.length==0) || (aTextField==null)) {
		return true;
	} else { 
		return false; 
	}
}

function isValidEmail(str) {
   return (str.indexOf(".") > 0) && (str.indexOf("@") > 0);
}
function checkForm() {
	if(IsEmpty(document.form.first.value)) {
		alert("Enter your first name.");
		document.form.first.focus();
		return false;
	} else if(IsEmpty(document.form.last.value)) {
		alert("Enter your last name.");
		document.form.last.focus();
		return false;
	} else if(IsEmpty(document.form.address.value)) {
		alert("Enter your address.");
		document.form.address.focus();
		return false;
	} else if(IsEmpty(document.form.city.value)) {
		alert("Enter your city.");
		document.form.city.focus();
		return false;
	} else if(IsEmpty(document.form.zip.value)) {
		alert("Enter your zip code.");
		document.form.zip.focus();
		return false;
	} else if(IsEmpty(document.form.phone.value)) {
		alert("Enter your phone number.");
		document.form.phone.focus();
		return false;
	} else if(!isValidEmail(document.form.email.value)) {
		alert("Enter a valid email address.");
		document.form.email.focus();
		return false;
	} else {
		return true;	
	}
}