You could try the Belkin USB to SCSI converter cable. It has a separate power supply to provide termination power.
We recently had to use one in a print shop where the owner didn't have enough money to buy a new scanner, and his 8100 running OS 9 was throwing fits when we tried to make an Agfa StudioStar work with it.
So, we crossed our fingers, hooked the Belkin USB to SCSI cable, and... low and behold, it worked when hooked to an iMac 333. But we did take the precaution of hooking it in via a separate, powered USB hub. When we tried it without the hub, hooking a Zip drive into the keyboard hub on the iMac -- crash city.
YMMV.
As a rule of thumb, the USB to SCSI cables only seem to work well with external HDs. We're telling people to upgrade their scanners to USB if possible, and if not, to invest in a SCSI card.
[This message has been edited by ESV (edited 03-16-2000).]