toniomac,
I have used a SCSI Zip drive on my Wallstreet with just the correct HD-30 SCSI cable. However, on the back of the drive is a switch for "Termination ON and OFF". If your devices have such a switch, make sure termination is ON if it is the only SCSI device connected.
Also make sure the SCSI switch on the back of the device is not set to '0' or '7'; those are used by the computer.
Are you starting up correctly? Connect the SCSI device > turn on the power to the SCSI device > start up the powerbook.
Do NOT hot-swap any SCSI device; all power must be turned off first.
Are you sure the SCSI cable is good? You want an HD-30 SCSI connector for the powerbook SCSI port that has 29 pins (pin #30 is missing; pin #30 is for SCSI Disk Mode only).
Try to get the SCSI HDs working since they should be the easiest; the optical drives may need drivers like Toast or PatchBurn.
Here is an article on SCSI devices:
http://docs.info.apple.com/article.html?artnum=13611