i just wanted to add my 2 cents.
last night (2-23-2009) i installed an ECLIPSE AVN-7000 (single din flip screen navi) into my cousins 02 es300.
all is true from above responses. you'll need the levinson faceplate, i hard wired the unit into the output of the factory amp (directly behind the glovebox) for all 4 door speakers. all power connections, and dimmer are available at the factory stereo plug. i did not want to spend 50-100$ on a "factory amp integration harness" since i was adding aftermarket amps and subs, so no need to retain the factory sub.
i also needed the VSS for afmkt navi. this wire is also located at the ECM which is directly behind the glovebox, next to the factory amp.
i did not try to use the factory brackets, with the metra "gap fiilers" for the sides. i actually used a HIGHLY MODIFIED 97-01 es300 kit. it really was not that hard to modify, just wanted to make it perfect. (ive been installing for 11 years) so for me it was easy, but the method described above seemed like it would work great. the 97-01 kit just filled the gaps great and allowed me to mount the head unit into the kit as opposed to doing an iso-din install. i will try to add pics as soon as possible. i will answer any question anyone has.
INSTALLING AN AFTERMARKET STEREO IN THIS VEHICLE IS COMPLETELY POSSIBLE!!!! NOTHING TO BE SCARED OF!!!