i was on the same mission over the past few days, hooking my carpc to my kenwood indash w/ touchscreen. this is what i've found out- in order for touchscreen to work with a component it needs more than just a/v inputs, it needs a serial/usb connection to transfer the touchscreen coordinates and such. some members thought i could tap into the ribbon cable on the touchscreen and attach it to the pc that way- but im not voiding my warranty on something so new.
so my resolution has been to add a usb touchpad to the center console. hope that helps.