What CD drive are you trying to connect to it, first off? Does the Portable have its original HD or do you have some sort of BlueSCSI or equivalent? What are you trying to install off a CD for the Portable, base system software? If using a BlueSCSI, can't you just copy what you need from the Legacy CD onto that and use it on the Portable?
Basically...what is it you are trying to do, exactly?