This is posted on another forum, so sorry to anyone who's had to suffer this more than once:
Right.. I tried my luck tonight and blasted ahead. I hooked up the floppy drive, found the power plug and the ribbon cable. Plugged them in to the mother board and grabbed the CD-Rom unit from the pile of stuff. I attached that in the same way as the floppy, plugged the EZ-VGA scan-doubler in the rear port, then inserted the mouse in the appropriate hole. I thought about hitting the power switch there and then, but I spotted the CPU, and , because I was on a roll, I stuck that in too, along with the Cybervision PPC card. Rummaging through the pile of stuff, I found what looked like 2 hard disks, one SCSI and the other IDE (I think). I found the Guru Rom SCSI adapter board and somehow managed to squeeze that in beside the other cards, hooked up the hard disk and power and hit the switch. Nothing happened for a while, then the hard disk started to click and whirr then stopped. I sat looking at the blank screen for a second then it changed to the classic 'insert floppy' screen. I rummaged some more and found a floppy with Work Bench 3.0 on and stuck that in. This is where we are now:

It's more progress than I expected, but I wonder if I maybe should have taken a bit more time
The CD-Rom drawer opens and closes, but nothing else happens and nothing is listed for the hard disk, though I'm assuming that because it clicked and whirred, the Amiga 'sees' it, therefore it's a good thing. Would that be right? I did find a floppy with 'GVP Faaaastinstall' on the front, but the error message said something about not having permission to write something or other. What next, guys?
Thanks for looking
cheers
Paul