Welcome to FT!
You need to go to a few sites.
1. Travel&Dining: Destination >> The World here at FT-
Do a search there with the word "tuscany" and "Italy"
2. http://www.fodors.com/forums/threadselect.jsp?fid=2-Go to their Italy forum do a serach and ask questions.
3. http://slowtalk.com/groupee/
They have an excellent forum. Make sure and visit other areas of there Slow Travel website. There are many reviews,tips and trip reports.

I travel to Italy as often as I can. Our next trip will be this Sept/Oct.
On a practical side,your trip is short for so much territory.
What time do you fly into Milan? You will need to bus into Milan and then take the train.
If you are planning on visiting the small towns of Tuscany you will need a car. I'd skip Florence and rent at Milan's airport. Our last trip we did just that. We stayed in a nice small town near Parma. We usually try and have a full day when we arrive so that we get to bed at 10 or so. Then we have no jet lag. We,however,didn't to drive all the way to Lucca (our first stop) on our first day.
The next day you can travel to Tuscany. I tend to break Tuscany into 4 segments: 1.Florence
2.Siena
3.North Tuscany
4. South Tuscan area
This is oversimplified,but traveling to the two main cities is much different than the hill towns of the north and south.
Rome,IMHO,is wsorth much time. I don't feel less than 3 nights does it justice.
With this little time,I'd skip Florence and Siena. I'd drive through Chianti and end up staying somewhere near Pienza or Montalcino and drive to Rome. Leave off your car there and then enjoy Rome.
You can also leave your car at Chiusi or Orvieto (nice town) and train to Rome.
I hope this helps start you off.