I can't Find an Option that in custom games where you can start off a game where One of your AI opponenets start off as your Vassal.

Maybe It's not in there But I'd like an option like that in a Game. Maybe in the next expansion or Patch.

I think there is an option to have an AI on your "team" for the entire game. Don't know if that helps.

You could go into world builder during your first turn for the same effect.

It is not an option under custom game.

"Finally, there is one other type of victory in Civilization IV, but that can only be achieved in combination with another victory type: Alliance Victory. In Civ4 it is possible both in Singleplayer and in Multiplayer mode to play a Team Game, or Co-op. In that case several players are part of a locked Alliance in which everything is shared: line of sight, Wonder effects, research (it's even possible to for two Civs in an alliance to research the same Advance to get it twice as fast) and territory. Units can be traded. Victory in this mode is also shared: if one of the players wins, his/her allies win as well."

"Finally, there is one other type of victory in Civilization IV, but that can only be achieved in combination with another victory type: Alliance Victory. In Civ4 it is possible both in Singleplayer and in Multiplayer mode to play a Team Game, or Co-op. In that case several players are part of a locked Alliance in which everything is shared: line of sight, Wonder effects, research (it's even possible to for two Civs in an alliance to research the same Advance to get it twice as fast) and territory. Units can be traded. Victory in this mode is also shared: if one of the players wins, his/her allies win as well."

Yea I know That Already But I think there is a Difference Between having a Vassal and Having An Ally