I just tried booking a hotel at the airport in Marseille and the only one available is the Hotel Balladins. Anyone know what is happening in Marseille that week that most of the better hotels are sold out already?

On our trip at Christmas last year we flew into Marsailles. It is very convienient and easy to get to Avingion.

The Rugby World Cup is on in France during Sep/Oct and Marseille is one of the major venues. I know because I have quarter-final tickets for the first weekend in October (Go Wallabies!!). Unfortunately, it will be very difficult to get hotels in/near Marseille around this time.

Do we need a car in the south of France? Or can we get around the south of of France with public transportation?

It really depends what you want to do. IF you want to see the countryside or smaller places, then you must have a car. If you only want to see the towns/cities, you can get by with trains. Bus lines are possible for some things, but schedules are limited and I wouldn't count on them for many things. I used a bus to go to Grasse when staying in Nice for several days, for example. I also used a bus to go to St Remy when staying in Avignon, but that schedules wasn't very convenient.

So what do you want to see and do? the answer depends on that. If you cannot drive or really don't want to, it is possible to book some van day tours to see some smaller places that are typical tourist stops (eg, Gordes) if you stay in a large city like Avignon or Aix. Of course, if you have a car, that affects where you will want to stay, as you won't want a hotel in the middle of a city like Avignon.

The OP went to France in September.

September of 07.