Devedon, parados,
Thanks to you also. I re-read your posts after sticking my head back inside the case, and perhaps it can be done, even with my skills. The real reason I was wanting to be able to boot from the old drive is because it has programs installed where I've lost the CDs or serial keys or whatever. No problem. I'll just have to save up some cash for new ones.
I'm going to have another attempt later today. The only drawback with Craven's idea which I've just realised is that I'm pretty low on funds and if I can get it inside the main case and save a purchase, that's fine by me.
There were a couple of things I noticed when I tried before.
1) Power - There seems to be a set of power cables (2x black, 1x yellow, 1x red) coming from the power unit, and linking all the other drives in parallel. Can I just put the new-old drive on any spare plug on the chain?
2) I think that the IDE-1 ribbon cable goes from the motherboard to the existing hard drive, then to the floppy drive. The IDE-2 cable is empty at the first slot, then goes to the CD/DVD drive. I put the new drive on this empty one? There is a diagram on my old hard drive which shows where to put the jumpers for different settings, but there isn't on the existing one. Do I need to change them both to cable-select, or can I leave them both as master, as the existing seems to be Primary Master, and the new one can be Secondary Master, with the CD/DVD drive as Secondary Slave?
3) My old drive is a Seagate one, so hopefully Windows should have the driver for it, as I gather Seagate are fairly common?
Thanks for your help. I'll come back with the results.