sub AuthenticateUser {
  my ($username,$password,$service) = @_;

  # this is my question
  if (DBI is not loaded and connected) {
    eval {  use DBI;  };
    if ($@) { die($@); }
  }
  # go on and do stuff with $dbh
  # select warp.username,warp.password,services.service
  # from warp,services where blah blah blah
  return($service);
}