In order to create your extruding box-like portions, you first need to split your front face several times. (see first image) As you can see, I have made an extra edge for the top part of the top box, an edge for the bottom part of the top box, an edge for the top part of the bottom box, and an edge for the bottom part of the bottom box. (4 extra edges total) All of this was done with the SpliPolyTool under the EditPolygons list.

I believe I explained the importance of snapping the vertices to the middle of an existing edge in a previous thread of yours. This ensures that the edge it srtaight and not slanted.

In the second image, you can see that I have created several edges going straight down to form the sides of both the top and bottom box-like portions.

In image three, I select the face for the top box-like part and the face for the bottom box-like part and extrude them outward. After that, I extrude again. Directly after I extrude this time, notice that you can either move or scale the extrusion. Scale it inward just a bit. After this, extrude once more and direct the extrusion into the inner part of the box so you can't see the face anymore.

The forth image illistrates what it should look like in the end.