Code P0420

Back in Feb 2007, I had a P0430 - Catalyst System Efficiency Below
Threshold 
(Bank 2).   Dealer replaced the MANIFOLD CAT CNVTR - LEFT HAND SIDE, that
is 
directly off the invoice, under warranty.

I now have a P0420 - Catalyst System Efficiency Below Threshold (Bank 1). 
Am I to assume there is another cat on the right hand side?  Also, is it 
right side from standing in front of the car looking to the rear or the 
right side if I was sitting in the driver's seat looking out?

Anyone else have this code and what was the remedy?

Thanks.
Dave