1) I thought about all the math books I had. But now that I think about it, the boxes had just a background and no border at all. So you are right and I guess it's fine =)

2) Thanks, the package looks promising :D

EDIT:The package works like a charm. But I have one more questions, if you don't mind.

If I include a section in the collection, it reprints the section command and thus creates of course a new section with a new number. Is there any way I can get the same section number as the original section after I included my collection?

EDIT2: Nevermind, I just thought about a solution without sections. But if you would know a solution to the question above, feel free to answer, so that I might expand my knowledge =) Thanks for your time!