I'm not quite sure in my mind quite how the security settings operate - seems a might complicated to me. However it seems that the drive was assigned SYSTEM control (not sure what that means). When I took ownership of the drive and all subcontainers and objects (which took the computer about 20 minutes to process), I suddenly had full access again.
I have copied what I need over to the new drive and as the old drive seems to be fully functional again, started to reinstall some programs to run from it - lesser used stuff which doesn't need to load on start up.
Certainly been a learning curve and I feel the security level might be set at a more manageable level for the home user editions of Vista.
Thanks for all help and comments
