Far from being a celebration, General Motors' 100th year in business is turning out to be one of the most wrenching in its long history. The Detroit-based company lost its spot as the world's biggest carmaker Toyotalast month, after hanging on to it by the narrowest of margins last year. It also faces the massive task of shifting its focus from the big sports-utility vehicles and pick-up trucks that have dominated its North American product line-up - and its profits - for the past 15 years.