linking vs import?

[ben]

I have a newly created db in which sample data is stored
in a table. My boss wants to be able to compare data
from a couple old database tables with the data being
entered into the new database table. What i would like
to know is what are the differences in linking the needed
tables vs. importing the tables? My boss said he wants
the old data added to the existing table...however, the
records in the old db have some identical sample ID
numbers and i dont know if that will cause problems with
an append query (i am TERRIBLE when it comes to queries
other than simple select queries)

any help with this will be appreciated.

Ben