Basic trigger question

I would like a trigger that does the following:

Whenever a record is updated or inserted into table A, insert a copy of
that record into table B, which is has exactly the same structure as table
A, except for an autoincrementing field which should get the next logical
value whenever a record is entered.

I'm sure this is a basic trigger problem, but I'm having trouble
figuringout the docs.

Thank in advance,

----------------------------------------------------------------
Travis Bauer | CS Grad Student | IU |www.cs.indiana.edu/~trbauer
----------------------------------------------------------------