Thanks for the pointers to VueScan.
It is certainly correct that one still requires the drivers for the scanner. I downloaded the trial version on both the XP machine and the Win7 one, and yes it will not recognise the scanner under W7. I can't find any drivers for it.
Works fine under XP Pro which I expected. Seems a perfectly reasonable interface but I have no real need for it as the original software does the job.
For a moment I thought I had a solution; I certainly won't be buying another scanner just because Microtek no longer support mine. I'll stick to my XP set-up for now, thanks.
Not entirely sure what a WIA driver is or whether I have one installed.
P.S. My Mac is still not connected to the HP....