I've decided that the solution to all my problems will be to partition my hard drive and install Leopard on the second one. Mac Pro early 2008, so it should be OK. This would give me back access to my LaCie external hard drive, and enable me to use the version of iMovie that I find an absolute doddle to use, i.e. iMovie HD 5.0.2, and in case I should ever want to use it, InDesign 2.
Are there any potential pitfalls?
Do you use all the drive bays on the Mac Pro? if not you could arrange the machine such that you have the first drive partitioned into two with different OSX versions in each partition along with all the applications. You then have the data files spread across the additional drives to optimise performance.
If you get SSD for your System and Application App file drive you would then speed things up dramatically.
Well, that was jolly interesting. Having partitioned it and tried to install Leopard it refused to do so. 'Click to restart your computer and install OSX Leopard on the selected drive' succeeded only in shutting it down. When I fired it up again I got the message, "You need to restart your computer, click restart or press the power button for a few seconds", which was not possible as the mouse was inoperable and the power button's behaviour has been changed by Mavericks.
The next time Apple offer me a free lunch I shall politely decline.
Served me right of course, for omitting to follow Euan's advice; I shall know better in future.
But guess what? A very nice chap called Tom (Mac Solutions) charged me a mere £25 to send Mavericks back to the Great Hard Drive in the Sky, and reinstall Mountain Lion, ha ha ha ha ha ha ha!
Now my LaCie Quadra works again ha ha ha ha ha.
Eric Jervis 