Thanks to all who offered suggestions aimed at solving this problem, some time after I posted my query, I found an unlikely answer on one of the newsgroups which was to replace the IDE cables with new ones, (and they had to be new as opposed to different), this worked, (and being both cheap and easy, was most satisfactory), and Chris and I have managed to install both Slackware and Debian now. It has to be said that in my case they are going in at an alarming rate until such time as I get it right!
When Chris opened up my case and replaced the cables he found that my rather elderly computer was in fact suffering from old age and neeeded replacing. I am having a `bare bones' computer built to take my new drives, and this raises a question, up to now I have followed advice I read somewhere that the swap space be twice the memory, (RAM?), having 64 whatever-they-ares of memory I have a 128 swap space, having ordered 128 memory, do I need a 256 swap space? All suggestions gratefully recieved, although I may be too old/full of pain killers to understand any explanation.
John