While your assumption is correct that both may be translated as "to include" into English, beinhalten may also be translated as "to contain" and einschließen as "to lock in". If you only wish to know the difference between the two words when they mean "to include", I would assume that they are synonymous, as I cannot think of an example that would support the contrary.

Hallo Huahua 87, hier sehen Sie Beispiele, damit der Unterschied klar wird: http://www.duden.de/rechtschreibung/beinhalten

You can check meanings of both words in a dictionary, for example: http://www.dict.cc/?s=beinhalten http://www.dict.cc/?s=einschlie%C3%9Fen