I know how to make I-maps themselves. I still am playing with how to get the best effect with them. I don't want to post incorrect info until I am more comfortable with the process. Maybe someone else can chime in with the I-maps if they have more experience.
here is a hint though as far as assigning. In milk there are 2 none buttons. Try assigning your regualr map to the top none and your I-map to the bottom. Then play with the specular lighting and diffuse. Then try assighning the I map to the top none and your regular to the bottom. See if there is any difference in lighting. It often is best to view your model in game because when you assign your i map parts of your model become invisible in milk.
This is what I will be doing until I find the best comination.
Thanks 3dot14 for converting that over