function isEmailValid(field) {  
  if (field.value.length >0){
    i=field.value.indexOf("@");
    j=field.value.indexOf(".",i);
    k=field.value.indexOf(",");
    kk=field.value.indexOf(" ");
    jj=field.value.lastIndexOf(".")+1;
    len=field.value.length;

    if (!((i>0) && (j>(1+1)) && (k==-1) && (kk==-1) &&
        (len-jj >=2) && (len-jj<=3))) {
      alert("The email address of \""+field.value+"\" appears to be invalid.\nIt should be something like yourAccount@yourISP.com\nPlease try again.");
      field.focus();
      return false;
    }
  }
  return true;
}