Well what can I say...
The difference between XP pro and Win 7 84-bit is quite remarkable.
I tried the training mission briefly with all graphics options set to default -except for the epilepsy filter and the game played really well, good frame rate -and you could see the rings in the sky -I didn't even know they were there before !
So it looks like the step up to win 7 and DirectX 10 has made a considerable difference.
The OS itself seems snappier than XP but still feels like a poor copy of OSX -it just feels a bit flakier and still not quite as fluid and responsive... It's not dreadful but I'm just glad that I don't have to spend the bulk of my time in its grip.
Worth it for the improvement in Games performance though !
Thanks for all the helpful suggestions, and for the laugh at the more tangental observations...
In fact I meant to say in response to Oldschool's comment about the Mac Users not knowing one end of a screwdriver from the other that one of the great things about the Mac Pro is that you don't need to use a screwdriver to change a hard drive !
Cheers