I think I may have solved the problem.
In the interest of exploring and learning about how my machine operates, I entered the BIOS mode (never done that before) at startup and found various settings for the drives. I noticed that on drive channel 2 the master was set to "CD/ROM" and the slave was set to "Off". Taking a chance I set it to "Auto" and returned to Normal mode.
When I checked the properties of the IDE secondary channel using the Device Manager I noticed the current tranfer mode for the "E" drive changed from "PIO" to "UDMA 5".
I haven't yet tried the iTunes, but my "E" drive is now significantly faster than it ever was before. It's the performance I was expecting , but never got, when I first had it installed.
Everything seems OK to me, but does anyone thinnk my solution may prove to be a bad idea in the long run? Is there a reason it was set-up as it was previously? Admittedly, I'm just poking around in the dark as I have no idea what any of these things really do so if you think I'm causing more harm then good, please let me know.
In the meantime, I'm off to test my iTunes and see how that runs. I'll report back my findings.
Again, many thanks to those who have offered advice. It was greatly appreciated.