Normally, news that New York City's oldest dog was turning 20 would be something we would read about and enjoy privately, like a good Robert Jordan novel or an Archie Double Digest we embarrassingly picked up at Duane Reade. But we have to share this with you: Paco Sosa, a spry dachshund from midtown, celebrated his second decade on Earth yesterday with a cake and a party with all his friends. Paco, who credits his longevity to organic meats and vitamins, is a firm believer in holistic medicine. Why do we feel the need to share this with you? Because this garish celebration comes on the heels of a tragic event in the small-pet world: Chanel, the world's oldest dog, died less than two weeks ago. Also a dachshund, Chanel lived nearby in Long Island. She was barely in the grave ten days before Paco seized the opportunity to start hogging the limelight. Is there no honor among wiener dogs?