second best solution...
It looks, after spending "quality time" with the oscilloscope, that there is no easy way to detect on the dock connector when the iPod is active (playing)
I can detect, pin 18 3.3V, when the iPod is docked but the signal is present even if the iPod is off (sleeping). The only bad thing about this is that i will not be able to just recharge the iPod and i.e. listen to the radio/CD. As soon as i put the iPod the radio will switch.
The other problem is that no available cable carries pin 18, i was hoping to use a cable obtained from an adapter like the belkin to avoid dealing with the dock connector.
I will research today if i can use pin 21, accessory indicator to detect the presence of the iPod. Technically it should be possible because the iPod can read the resistance value on that pin to ground to detect the type of docking unit, but it may be a very small signal... the good thig is that that pin is available in the belkin car cable.