Heeey, is I Ching JUST a book that makes predictions? Some sorta chinese tarot? Isn't it supposed to have deeper philosophical undercurrents and be maybe even the founding legend of Chinese civilization etc?
It is both a book of fortune telling and philosophy. The basic premise is that all things are the manifestation of two opposing forces, Yin and Yang, which are the manifestation of the Great Ultimate. Each thing in nature contains layer upon layer of Yin and Yang. The Yi Ching goes up to six layers, thus considers 2 to the 6th power (2 because there are two possibilities, Yin and Yang; each power is a layer), which is 64. One can extend this infinitely.
People who use the Yi Ching to tell fortune believe that one can, through some manipulation of stalks or coins, calculate these layers of Yin and Yang to derive some symbols known as "Gua", which contain these Yin and Yang lines or "Yao" (each line is a layer.) With these Gua's and Yao's, the fortune teller can see the forces of nature and tell what will happen. Yi Ching became a philosophical book with its underlying premises concerning laws of nature.
As a book of philosophy, its interpreters seek to use it to explain the structure of the universe, metaphysically and physically. The idea that Yin and Yang are the manifestation of the Great Ultimate, the two forces are manifested in a myriad of things, is one example of philosophical interpretation of Yi Ching, which sees in the universe a stucture of oneness to many, of 2 to the 0 power to 2 to nth power.
The Yi Ching is a very important classic to both Confucians and Taoists. It is considered by some as the most ancient classic of the classics.