Descramble a noob please! Prius'04 a/v system?

Hi there. I'm a happy owner of a cherry 04 Prius. Unfortunately, USA model, thus - miles, gallons and other weird units, plus unusable navi (well, I do have a hacked disk with Russia, but no voice guides and no Cyrillic - so it works mainly as screensaver), bluetooth etc.

Nearest plans: iPhone integration plus backup camera and parking meter.
Farther plans: human-readable units, working navi.

First questions.

Video input: how's it done?? I heard (from Japanese right-handed car owners) that there's a TV tuner under the rear seat that not only shows TV, but also provides a socket for the cam. But USA/Euro models surely do not have it. I heard also (from local servicemen) that there needs to be a hardware hack that allows the head unit (MFD) receive the AV signal directly. They charge A LOT for a small PCB, and I'd like to avoid extra expenses. And finally, third thought: an AV to RGB converter inserted BETWEEN navi and MFD. Where is the truth? What's the ideology of the MFD in terms of video input?

Well, that was the first part of the question If I'm going to install a third-party navi, or a parking meter with digital distance info, I'll need full-fashioned RGB (VGA? Component?) inputs. How do I reach those, how do I switch between inputs? I'd LOVE to have a function diagram of all that jazz!

iPhone/iPod etc. I believe that usaspec's PA20-Toy (which I've already bought on ebay) will work ok. The question is... what is it being plugged into? The MFD or CD changer? If the first, then won't it interfere with AV/RGB interface?

And finally, metric system. Do I need to re-solder the EEPROM in the MFD like our servicemen do (again, for PLENTY of money), or there is a 'civilized' way to re-program the computer using just the car's AVC-Lan or some diagnostic port? I'm a sysadmin, so having RTFM once, I'm pretty sure to not mess up with something. Is there a known way?

Thank you for possible answers and (yes, yes!) howto links.

 

I can only repeat that it HAS been done, by reprogramming (and, unfortunately, resoldering) two EEPROMs in the head unit. This will cost me fair $300...

Pity it can't be done in software-only way.