Compare two Microsoft Access databases

"Below are three free products that might help.

Free Database Compare 2.0 :

The StarInix Database Compare
application will allow you to compare
the structure of two databases and
display all the differences between
them. Supported databases include: SQL
Server (All Editions), MySQL and
Access databases. You can compare two
different databases, like access and
SQL 2000. It will also allow you to
create snapshots of a database and
compare a live database to an
snapshot. A database structure viewer
is included.

Compare'EM Lite

A very simple to use utility to
analyze a pair of related Microsoft
Access databases, determine what has
changed from one to the other, and
generate VBA code to propagate those
changes.

Total Access Analyzer

Total Access Analyzer examines all
your database objects to provide
extensive documentation,
cross-reference, and application and
flow diagrams, with over 350
presentation-quality reports.

EDIT : Please remember that this answer dates from 2009 before downvoting it."

"Try the free version of AccDBMerge.
Be aware of the following restrictions though:

AccdbMerge Free provides basic data diff and merge facilities with the
following limitations:

both tables must have compatible primary keys,
no more than 50 fields in each table,
no multivalue/attachment/binary fields.

Pro version does not have these limitations. Also, it allows to compare data between files with
different security options."