Luis, i think the previous posters missed the part about 8 days EXCLUDING travel time. I take this to mean you will be there for 10 days minus your arrival day and minus your departure day. In that case 8 days is enough time.
I assume you are flying in and out of Rome. If you arrive in the morning then I would head straight to Florence. For first time travelers to Italy, I think Rome and Florence are a must. Spend a day or two in Florence and then go stay in Siena. Siena is a good home base to explore Tuscany. From there you can take a bus tour of a winery or rent a car and spend a day or two exploring the area for yourself.
After two nights in Siena, head to Rome to finish off your trip. You should spend at least 4 full days in Rome. My suggestion would look like this.
Arrival Day - go straight to Florence
Day 1 - Florence
Day 2 - Siena
Day 3 - Siena
Day 4 - Travel to Rome (you could also spend another night in Tuscany, your choice)
Day 5 - Rome
Day 6 - Rome
Day 7 - Rome
Day 8 - Rome
Departure Day