reuse of schema

Does anybody know of an example
showing the reuse of a schema (defining its own targetNamespace)
within a covering schema (defining a different targetNamespace).

--the task:
there is an existing schema which can be used for validation of complete 
xml files.

Now I would like to apply the same rules to an element of a covering, 
bigger xml structure where the former root name now becomes the elements 
name.

The inner schema should keep its structure while be use by the covering one.
--end of task

I played aroung with <xs:include/> and <xs:import/> without success. 
<include/> looked like the wrong way. And <import/> won't be processed by 
the validator as I understood it (my be wrong). So - if there is a working 
example I could start from there.