Using Headphone and no cds....

HI all !
2 questions:
1- i have a mac without cd in it, how am i supposed to do to obtain Cross DJ ?
2- how am i suppose to monitor each track before lauching them considering i have only one headphone plug on my mac which is supposed to be used as my main audio output ?.....
THX
2 questions:
1- i have a mac without cd in it, how am i supposed to do to obtain Cross DJ ?
2- how am i suppose to monitor each track before lauching them considering i have only one headphone plug on my mac which is supposed to be used as my main audio output ?.....
THX