Ok, i got the microphone working finally with VoodooHDA-By-Thireus.zip from
http://thireus.dareyourmind.net/ !
Still GarageBand is working a bit weird, with no microphone plugged in, it complains about feedback, and always asks to turn off monitors (speakers?) or keep them turned on with feedback detection. Also the tuner doesn't seem to be able to detect the sound of my classical guitar well...But other than that, it's perfect, i can record audio fine in AudioHijackPro
Cheers