I agree with cfitz on this one. I would not recommend using an IDE cable longer than the specified 18 inches. Using a longer cable can result in errors and in the worst case, data corruption. If the errors can be successfully repaired by UDMA CRC checking, it will at best slow down the data transmission.
Your idea of adding a controller card is a good one if you want to retain all of the devices and it will solve the cable length problem. They are relatively inexpensive and will add flexibility to your setup. It is usually best to use the controller card for the hard drive(s) and use the motherboard connectors for other devices.
If it were my choice, I would remove the Zip drive. They have a well deserved reputation for causing conflicts, especially with DMA and CD-RW devices. The discs are expensive, data throughput is slow, they hold only a fraction of a CDR, and the Zip drive is obsolescent at this point. With a CD-RW drive, you really don't need the Zip.
EdT wrote:Incidently, I'm now advised (Dell Forum) that it's best not to use the same EIDE cable to connect the burner and the Hard Disc to the motherboard
You don't need to buy a controller card, just get a longer cable, you should connect the HD(Master) and DVD(Slave) on IDE1 and the CDRW(Master) and zip(Slave) on IDE2 Your HD will be limited to UDMA33 because of any of the optical drives. I'am using the same setup without any problems.
There is no problem in connecting the burner and hard drive on the same cable unless you get buffer underruns with this configuration. You can try experimenting with different configurations to see which works best for you.
Your hard drive will not be limited to UDMA 33 if it is connected to an optical drive. It will run at its full rated speed and so will the ATAPI drive. Modern computers use separate device timing for each device sharing an IDE cable.