merging databases

I have an Access 2003 database containing about 150
tables. Almost all of the tables use an autonumber field
as a primary key. How do I merge records from two copies
of the same database from two different users? The
problem is that the autonumber fields will overlap. One
solution I thought of is to use a two field primary key
for each table where one field was an autonumber field
and the second field is a unique user id. Is this the
only way to do it? Are there better ways?

Thks Miles.