Dear Colin Thanks again. My apologies for not replying before -among other distractions, Microsoft is suddenly trying to claim that my W7 is illegitimate and has blocked the registration key - I bought this W7 from them, so I can understand their concern... Anyway my thanks for all the work you have put into clarifying what I probably ought to have been able to work out for myself, and at least I am better informed if no less an idiot. Best wishes, Andrew