Here is an excerpt from
http://www.locksmithcharley.com/toyota-obp-e-instructions.pdf

Of primary importance is determining if you have a key that is enrolled in
the car's computer as a "master" key
or a "valet" key. The procedure for making this determination is:

1. Positively locate the "security" or "anti-theft" light. This light should
blink when there is no key in the

ignition or if an unrecognized key is placed into the ignition.

2. Insert the key you have into the ignition - DO NOT TURN ON. There are 3
possible things that may

occur:

(a) Security light continues to blink = unrecognized key.

(b) Security light goes off IMMEDIATELY = MASTER key

(c) Security light remains illuminated for 1-3 seconds before going out =
VALET key

.....................................

So first hold the key holder within one inch or less of the ignition, put
the flat key in while watching the security light, and see if the light goes
out immediately. If it does, then the flat key and holder combined will
enable you to program "real" keys. But you would want to delete all previous
keys for the car first, as stated on the same website. The computer will
only accept so many programmed keys.

There is more good info on that website regarding do it yourself key
programming.

Also, if you can, like me, live without a key with buttons, you can order a
NON-remote master key from Lexus, using your VIN,

http://lexus-parts.com/partlist.asp?SubCategoryID=22&ModelID=5

for, now get this, forty nine bucks!!!

I ordered two for my 2000 ES300 when I had to get the engine computer
re-flashed. I had to pay $61. But WAAAAAY better that $250.

Now you tell me, are bottons on a key worth $201 plus tax more than a key
WITHOUT buttons? I say NO WAY!!!