Allegro means "Allegro Low-Level game routines" and tile stuff is high-level. Allegro just allows you to load, create and draw bitmaps, but doesn't provide any "tile map" functionality.

The Allegro.pas' demo game does use tiles, but the engine was written from scratch. Anyway you (Darkhog) should take a look into the sources (tilemap.pas and sprites.pas). The sprites unit shows how to calculate the "tile ID" from the sprite position.