You can use either, Denso(Iridium IK20 or PK20TR11 ND), or NGK(BKR6EKPB-11) spark plugs in your 1997 ES. These are OEM plugs. Bosch Platinum plus are NOT OEM, but that doesn't mean that you can't use them. I suggest calling your Lexus dealer to find out what type they recommend and then go to your local auto supply store and ask how much $ they sell them for. :)
Alan