Pipoufle said:
1- How the cultural expansion over an opponent territory works ? I tried to understood the way my boundaries will push my neighbour's ones back, but it seems not so easy... And in the same ways, when an opponent city will enter in a riot ?
Each city spreads influence (or culture, that's just two words for the same thing) in a circle around it. The radius of this circle increases when the city reaches a new cultural level. Tiles in the center of the circle receive more culture than tiles at the outer rim.
Regarding the pushing back and forth of boundaries: Each tile accumulates this culture which is spread by the cities. So, each turn, a tile may receive a lot of culture from one of your cities, a little less culture from another one of your cities, and some culture from your opponent's cities. The tile "belongs" to the civ which has accumulated the most culture on this tile. So, if you continue to spread more culture on tiles as your opponent does, eventually they will flip to you.
Cities may riot when their own culture is in the minority in them. However the city garrison often prevents a flip.
You can see who owns a tile (and how much percent of the total culture on this tile he has) by mousing over the tile. In the lower left you'll then see it's owner and the culture percentage.
Pipoufle said:
2- IDS is called "team project". What does it mean ? How many civs can build an IDS ?
Teams can either be fixed when setting up the game, or they can be formed by accepting alliances in the game (when this option is checked, it's unchecked by default). A team project is a project from which the whole team will profit, although only one team member built it. For example, if you and another civ form a team, then you build one space ship together.
Pipoufle said:
3- What is the difference between a cease-fire and a peace treaty ? It is also indicated that peace treaty will last 10 turns... What is the sense of that ? Diplomatic malus if war is declare again before ?
You simply cannot declare war in the ten turns when a peace treaty is in effect. I don't know exactly about cease fire, I think it's the same as a peace treaty, but with no fixed duration. But that's a guess. I never use it.