Failure To Start Game

i have been watching a bunch of minecraft videos for a few months now, deciding whether to buy it or not.. and i am choosing to buy it, so u'd think that i'd try the demo first before i buy it so it will be compatible with my mac. i logged on minecraft.net to try the demo & it kept crashing – i already have 7 crash files on my computer and it took me already an hour to locate them. i really hope this gets fixed or else i can't play the game. i just can't get the demo game to start. please fix it soon so i can buy the game without any troubles.thanks!