Also, if I remember correctly, it has to be an Apple ROM'ed drive. if its not, it wont boot. 

And that old of a machine, the "C" key doesnt work. You need to hold the key-combo for the SCSI ID.

Worse case scenario is un-bless the system folder of the HDD by moving one of the system files out of the folder. 

Then try again, it will see the CD and boot from it, ONLY IF the drive is good, and its apple ROMed