The Boolean modifier hierarchy has changed with v7.
First comes the parent object you want to add/subtract/intersect other objects. Then add the Boolean modifier to it.
Then add the child objects to the modifier.
Is this working for you? I have no clue what your mesh should look at the end.
I am attempting to add a simple box to another object.
I have tried both boolean operations(Creator and Modifier). I think there must be a problem with the base object which is an .stl file I downloaded from Thingiverse.
Base object is first image, base object and box is second image. Third image is operations I have tried. I think I have the hierarchy correct.