MartinBollerup:
I burned a ATMEGA-chip earlier today and I'm down to my last so for once I don't feel like experimenting toooooo much - any help is warmly appreciated.
Thanks,
Martin
Your circuit is capable of sending up to 12 volts into the Arduino analog input pin when the maximum voltage should only be 5 volts (that's why you're burning out your AVR chips).
Connect the potentiometer to 5 volts and ground (not 12 volts and ground like you have).