Hi!

Since your family will be living in France, you will be considered as a French fiscal resident. You can take that as a certainty.

Impôt sur le revenu : notion de résidence fiscale

That means you will have to make a calendar year Income Tax declaration of your world income in France per end of May of the following year.

For 2008, you will be required to declare your world income, from August 2008 ytill 31.12.2008, and that by 30.5.2009.
In France you do not get automatically tax forms, unless you have made a previous declaration. So that means in time you will have to fetch the forms 2042/2044/3916 ( and possibly others according to your income ) and fill them, and send them to the local Centre des Impôts ( not the Trésorie, which is only competent for collecting taxes ).

If you pay taxes in other countries, you declare gross and the taxes paid so that in most cases, if their is an agreement between the countries you are not taxed twice. NB. For financial income, you would pay in France in most cases.

Yours,

giantpanda