One short update to the last post – after swapping the Iomega drive for the LaCie unit shown in the photo, I started to have problems putting the Mac to sleep. Every time I put it to sleep, it waited a couple of seconds and sprang back to life; it would then continue cycling every few seconds between sleep and life until it got bored and had a kernel panic (in other words, the operating system crashed).
After reapplying the latest OS X updates and having searched the usual Mac support sites (including Apple’s own support site) the problem persisted and I was none the wiser. It was clear that ever since the beginnings of OS X there have been weird and intermittent problems with external firewire and USB devices and after quite a bit of experimentation, I discovered that changing the Canon LIDE 80 scanner and a D-Link USB hub from being attached via the LaCie unit to direct attachment to the Mac, the problem went away.
On a similar note, I have also discovered that if I run Windows 2000 under Parallels on the Mac mini, Windows doesn’t detect the ENTER key being used if my Microsoft trackball is attached to a USB port on the Apple keyboard. Attach it to the LaCie unit, and all is well.