Zidane said he told him to stop pulling his shirt, and that if he [Materazzi] really wanted it, he'd be happy to trade at the end of the game. After that, Materazzi said something involving Zidane's mother and/or sister, but Zidane didn't say the details of what was said exactly. He added that he had to listen to it once, twice, and that at the third time, he got sick of it, because he could only take so much verbal abuse. That's when he hit him.
About the headbutt, Zidane said he wanted to apologize to kids and mothers, and that it was unexcusable/unforgivable, and that it should be sanctioned. However, he added that what he did was a response to a provocation, and that the one who provoked it should be sanctioned aswell.