Well, thank you all, particularly Steve and Bob, for all the tips. I've just taken delivery of a new Dell Studio 15 portable and apart from the loudspeaker sounding like an earpiece lying on a desk with volume turned up to max, several times over the last couple of days PE7 has died with a display problem. Unfortunately the 'recovery' message only appears for a short period of time before PE7 gets blown away. I'm hoping all these tuning etc ideas will at least reduce the frequency of that problem.
My wife's portable is a one year old Fujitsu Siemens with slightly inferior specs by comparison to the Dell and I never needed to 'tune' it - it has just worked for PE7 flawlessly.
I'm working round the Dell loudspeaker problem by having a speaker plugged into one of the headphone sockets otherwise editing would be out of the question. Obviously that problem will have to be addressed by a technician in the next few days. I'm really shocked that Dell sent out a machine with such an obvious fault.