Just put the Imobile Units files that you downloaded and put them in the Ai folder thats in:
C:/Program files/Microsoft Games/Age Of Empires II/AI and put them there...
Than go into the editor go to players, select the 'Personalities' and select Imobile Units AI file that will appear.
EDIT: Typo
[This message has been edited by Dark_Reign (edited 05-14-2005 @ 02:33 AM).]