You no longer need a hacked civ3edit with the last patch if you do not have it get it.
You need to alow a civ to build it in the civ box on the units tab (hold down Ctrl to select multiple Civs).
You can build it when you get the tech (leave on none to test).
If you add a new unit you must have a folder with the name of the unit in the ..\Civilizations III\Art\Units folder with a unit.ini file in it (the unit, folder, and INI must all have the same name.
You have to load the edited BIC in Civ3 (save as something other then your Civ3Mod.bic in the Scenario folder and load as a Scenario).