what's the difference about ADC and DVI? is it DVI apple brand or a better quality? is it necessary for the apple 100$ swich for DVI-ADC? saw a cable that changes ADC to DVI or VGA is the quality bad if I use this type of short cables? just like the DVI to VGA that comes with the Al 15". what about using the ADC to VGA? or use ADC to DVI and DVI to VGA (both short cables)? Can I use the DVI connecting and use DVI to VGA instead of using the ADC since i don't have an apple display or I must use the ADC as the primary.