How come my Power Mac does not show the hard drive?

Hi, I have a power mac that i have been meaning to fox for a while, so i decided to, just had to install the operating system, so when i insert the CD (BTW its a macintosh) , it read perfectly until it reaches to the step where it says, SELECT A DESTINATION TO INSTALL THE MAC OS X SOFTWARE, and i cant see my hard drive that i have connected to my computer, i tried with multiple hard drives but nothing works and it is very frustrating because ive tried everything, so if anyone has an answer to my problem please write it in, i very much appreciate the help. THX