tourist visa

Hi

I'm asking this under the assumption that there are no stupid questions, just stupid people (and I'm ok with the fact that I might be one of them! %-P ). I am planning to go to Spain to wwoof this summer (volunteer on an organic farm). I understand that as a citizen of the United States I am allowed to be in Spain for 3 months without obtaining any kind of work or residency permit. I wanted to stay longer than that and was planning on just hopping over the border at the end of three months, getting my passport stamped in France, and then coming back for another 3 months. Then recently I found out that a United States resident can only be in Spain for 3 out of 6 months (i.e. at the end of 3 months one has to leave the country for a full 3 months before they can return), thus putting and end to that plan. For a few minutes. Until I decided to ask if anyone here could tell me just what are the penalties for overstaying your tourist visa? Do they really look at the date you entered when you leave? If I show up with a return ticket leaving from Madrid dated 5 or 6 months away, and tell them that I'll only be in the country for a while and then I'm going to travel around and then leave out of Madrid will they send me home? Secondly, Does anybody know: If I were to leave Spain after 3 months and go to Italy for 3 months, then come back to Spain, would Italy let me in and would Spain let me back in? If someone could clue me in I would greatly appreciate it. Thanks,
AG