String.prototype.isvalid = function(){
 return !!this.match(/^([a-zA-Z0-9]{1}([a-zA-Z0-9\.\-\_]*)[a-zA-Z0-9]{1})@([a-zA-Z0-9]{1}([a-zA-Z0-9\.\-\_]*)[a-zA-Z0-9]{1})\.([a-zA-Z]{2,4})$/)
}



function dropdown_validator() {
 if (document.form1.fname.value=="") {
  alert("Please Enter Your First Name.");
  return false;
 } 

 if (document.form1.lname.value=="") {
  alert("Please Enter Your Last Name.");
  return false;
 }
else if (!document.form1.email.value.isvalid()) {
  alert("Please Enter A Valid Email Address.");
  return false;
 } else {
 return true;
 }



}


<!-- Begin
function popUp(URL) {
day = new Date();
id = day.getTime();
eval("page" + id + " = window.open(URL, '" + id + "', 'toolbar=0,scrollbars=1,location=0,statusbar=0,menubar=0,resizable=1,width=420,height=250,left = 376,top = 357');");
}