First off, its good that the solution is open for everyone to see, so ill eply here.
To add two materials to one object, select the faces you want to have a different material(in edit mode), then go to the materials and click the assign button under the big box with the material names, do this when you have the faces AND the material you want selected.
To take the rims out just select them in edit mode and press "P"
This will separate them from the object and make a new one. To join them again, select bothe the rims and the rest that were connected to them before and press "CTRL+J"
That will merge them into one object again
Hope this helped
If not ill try better next time ^^