Actually, that feature in only available in Age of Empires II: The Conquerors Expansion. Without that, you're stuck with 75 people.
You can create units using triggers, and for a good trigger tutorial go to the AOK Heaven Blacksmith (scenario designing section), and go to design articles, and it should be there.
Nakul.
[This message has been edited by Nakul (edited 09-15-2000).]