Thanks for the advice but, I've tried the bang up-to-date but uncertified drivers that came with it, the otherwise stable 185.85s and the last WHQL 258.96 all to no avail. (All stable with the 7600!)
Also this version of the card has only ONE power socket.
The card WILL be sent back for a full refund and I will buy a relatively cheap 9200 or such from my local PCWorld as a stopgap until I shell out for a new PC entirely! I've never had a driver problem before in 4 years with Vista etc regardless of uninstalls etc. Each time I throw the 7600 back in and there's no problem.
(Please correct if wrong but Vista creates separate folders for each driver iteration?)