A separate bibliography for each 'chapter' of a document can be provided
with the package chapterbib (which comes with a bunch of
other good bibliographic things). The package allows you a
different bibliography for each \included file (i.e., despite the
package's name, the availability of bibliographies is related to the
component source files of the document rather than to the chapters that
logically structure the document).
The package bibunits ties bibliographies to logical units
within the document: the package will deal with chapters and sections
(as defined by LaTeX itself) and also defines a bibunit
environment so that users can select their own structuring.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=chapbib