US citizen travelling between Schengen Countries

I am an American. I have been in France since late April 2008 until the present, beginning of November 2008. I realize that I have outstayed the 90 days in 180 that I as an American may stay in a Schengen country. However, I would like to leave France for a few weeks to visit a friend in Italy, also a Schengen country. My question is thus: will I be obliged to pass through Immigration and present my passport upon my arrival in Italy and/or upon my return to France? And if so, will this be problematic? Would it make any difference if I travel by plane or train? Thanks in advance for any advice you have!

Travel without internal border controls within the Schengen countries. Temporary reintroduction of internal border controls possible. The visa limit is applicable to all countries within.

thank you Vinny.