external cd config problem?

I recently bought an used external cd and cannot get my computer to recongnize it. I have it connected directly to my computer and off of the cd I have my zip. Any suggestions? The only software that came with the cd is CD-ROM Toolkit. I am running a Performa 575 which has an internal cd - could this be the problem? I NEED HELP!!!

Did you install the CD driver software? Is the device terminated and given a unique SCSI address? Those would be the two areas that I would look first.