Do you have what it takes to be a Su Doku Grand Master?

Su Doku, "the crosswords without words," come with a warning: it is seriously addictive. You don't need to be a mathematical genius to solve these puzzles; it is simply a question of logic and a little patience. Here is a collection of 100 new puzzles arranged according to difficulty, starting with the easiest and ending with the fiendishly difficult.