One more note....

I just finished a 3 week vacation in Italy and never had a car. I took the train from city to city, and sometimes a cab from the train station to the hotel. Once you're in your destination city, you'll have little use and little want for car. So save the expense (and hassle) unless you plan to do a lot of day trips to other towns while using 1 city as a base for several days. If it's a short drive from Venice, then it's probably a short train ride. And the trains are amazingly cheap. I had 10 train trips that cost me less than $170 total - and I was all over Italy!