You need to use selection sets. For example, if you had a cube, you would make it editable, then in polygon mode select one face. Then choose set selection from the selection menu (right at the bottom). A red triangle will appear in the object manager to the right of your cube object. Now drag the .psd material onto your cube in the object manager. Now in the texture tag properties window you will see a field called Selection. Drag the red selection set triangle onto that field. This will now restrict the texture to that polygon/face. Do the same with all the other faces using your different textures.
Badly explained, but I hope you can follow my ramblings.
Mitch