Car computer power supply

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Hi, I want to build an ATX power supply for a miniITX computer to power an MP3 player for a car. I figure this is the best place to post :)
I am not too concerned with efficiency for now... so I am content with a simple virtual ground power supply with voltage regulators to smooth out and give accurate votlages.
I am thinking of using the main power supply (bypassing ignition) to supply the power supply and will be switched on by the switch (see further down). There will be a constant supply of low voltage to allow the computer to suspend to RAM.
My other idea was to use the remote wire to act like a power switch. There is a problem with this that I can't solve. I need a switch which shorts when the voltage changes. So car is off, remote is 0v. Turn car on, remote is now 12v and it shorts the switch momentarily acting as if someone was turning the computer on.
Then when the voltage goes back to 0v, it will momentarily short the switch acting as if someone was pressing the power button.
 
Does anyone have any circuit schematics or ideas on how to implement this? I tried searching for flip-flops but I don't think that is what I want.

Also, has anyone made their own ATX power supply for a car? I have searched on google plenty but can only find AT power supplies.
I only need lower power, in the order of 40W max.

Mike
 
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