Author's Note: The Chinese animal-zodiac goes through a 12 year cycle. For example 2001, the year Bush took over, was the "Year of the Rat" ;) ... and 2006 is the "Year of the Dog".
In Asia it's mandatory etiquette to send a New Year's / Season's Greetings card to all one's friends and business aquaintances.
Aside from the Escher-style arrangement of the dogs, there's also deliberate cleverness hidden in the number of dogs. There are 18, representing both "heisei 18 nen" (18th year of peace, the way Japan counts years) and also representing 12 months + 6 years (as in 2006).
The writing on the left says "Heisei 18 nen, inu" which means "18th year of peace, year of the dog". The 4 other characters say "Spring, Summer, Autumn, Winter" and are surounded by colors matching the seasons.
Each dog is numbered except for #1, which is simply labelled phonetically "wan". This's a pun on the sound of "one" and on the onomatopoeia "wan". "Wan" is the Japanese equivalent of "woof".