Go to the general in Dido's palace. (He's in a hidden room.)
Ask general boatmaker.
Ask general bireme.
Hunt the architect in the boatmaker's cave.
Ask architect plans.
Help the Carthaginians
Return to the general.
Give plans general.
» ...played an important role in building up Carthaginian naval supremacy.
Help the Libyans
Hunt the Libyan spy on the plains of Megara,
Give plans spy.
» ...is a traitor to the Carthaginians
You can get both whoises by using somebody else's plans. The Carthaginians don't seem to care if you're a traitor.