Its ok Ive found the handbrake cable switch, its next to, well the handbrake duh, hidden underneath the centre console. now connected.
I had to partillay removed the top part of the centre console from the astry, so I could run the green parking cable from the new stereo/DVD and wire it to the handbrake switch.
Anyway what the Green parking cable does is use the handbrake like an on off switch or ground, so for example whilest driving/handbrake disengaed, the DVD wont play, but when stationary/handbrake engaged the DVD can play. Obviously this is a safty feature. Ive read on the internet alot of people had bypass this, so the DVD plays whilest the Car is in motion. But why do this!, its dangerous and very distracting! even if its just for your passengers to watch, you just cant ignore looking at the screen, its in front of the driver!
So be safe all you have to do is connect the green cable to the parking brake switch, its very easy to do.
My new DVD/Stereo is a Pioneer AVH-3100 for £279, I purchased from here http://caraudiosecurity.com/shop/product/products_id/10919.htm
The sound is brillent even on Stock Lexus speakers! what a difference in quality. excellent bass and treble.