Update.

My cheapo 'bought-from-ebay-shipped-from-hong-kong' firewire card is now installed and the problem seems to be fixed - I captured a whole 1hr DV tape last night.

Just goes to show you - £30 Belkin USB/Firewire combo card won't work but £3.50+postage firewire only card works first time on VS9 default settings.
When I think of all the wasted hours trying to get the Belkin to work....

Thanks

Glenn