Thanks. Very interesting. Not least because what kicked this whole thing off was the graphics going completely banzai:
I decided (after any amount of diagnostics, anti-virus, reinstallings etcs) to cut my losses, nuke the thing with Dban and stick it on
ebay. Except that when it woke up after dban, the screen was clear. Which is when I started laboriously rebuilding it.
Having completed it, I returned it to my eldest, who was delighted - for about 20 minutes. Then the graphics went back to square one. *sigh*
I notice the last poster on that thread you kindly linked to said the Vista drivers would 'probably function under Windows 7 without any additional work'. I don't suppose it would be worth trying them with XP? (Or is this, as I suspect, basically a hardware fault, and no amount of software fiddling is going to make any odds?)