Thanks for your reply and, more so, for the link to the driver. You're right, I hadn't installed it. I thought I had but the one I had installed was the one for the onboard graphics card.
As for the 'problem' yes, I am still having it. I tried to set the resolution to 1280x768 through the NVIDIA control panel and the screen went off on one exactly the same as before.
However, having messed about the NVIADIA control panel a bit more, I set it to 1280x800 (one up from the one I wanted to put on) and it looked terrible. So I can only guess that, if I had been able to set it to 1280x768 as I wanted to, it would have looked even worse? So I've resolved myself to the fact that I'm going to have keep it at 1280x800 with the Icons set to Large and Test to Large also. I'm sure I'll get used to it.
So, thanks again for your help and please give my regards to Alberta. It has been a long time since I covered 'most' of it (or it seemed like it at the time) on foot one summer 35 years ago!