sync two databases

Hi,

I have two databases (8.1.11) where the content of some tables should be
synced nightly. I tried to dump the contents with a script (similar to a
pg_backup script), and then load them again, but there is a DROP
statement in the dump, that doesn't work on restore since there are
dependencies between tables (restore says I should use DROP CASCADED,
which I don't dare...). Is there a way to only dump the data? I can't
seem to find the respective parameters in pg_dump documentation.
Another thing: I have seen that database grow to 48Mio rows in one table
(I didn't do the design ;)), so I'm afraid a standard dump using "COPY"
could give me problems later on... though a "INSERT" is said to be slow?

Any ideas on this?