The critter is an old attemp to make a liker from the Biohazard game.
As far i know, you cannot apply the texture to only one poly. If you make the poly as an independant element you can.
Do you mean apply a diferent texture of the whole object or apply the same but another part of the texture?
Next lesson will be editing the UVW map, so you can adapt the texture to the model.
You can select element, poly and vertex to move selecting "Editable Mesh" below "Aurora Trimesh" in the "Modify" tab.