nooby q: how get a row just inserted?

I am probably breaking the rules here which is why I have a problem, but
here goes: I am trying to build an audit trail skeleton of all my table
inserts. Everything table has a column for the serial ID of an audit
trail table row I will create for each transaction or batch of
transactions if I like. My problem is that the audit trail table as I
conceive it does not have a natural primary key. I do have serial id and
timestamp columns supplied by PG, but being supplied by PG I need to
read back the row to get at their values.

If I were using OIDs on the table I realize the insert returns the oid
created, but (so far) I am not.

Am I going to have to use oids or fake a distinguishing column I can use
to read back an audit trail row just after inserting it?

I was hoping there was some select magic that would let me insert a row
within a select which extracted the PG-allocated serial id column, but I
do not see anything like that.

kt