I got an answer from Samsung technical support
"In order to allow for compatibility between the Windows 7 computer and your phone you must download from the Microsoft website VIRTUAL WINDOWS XP. Please be aware that this will only work for Windows 7 64 bit Professional, Enterprise and Ultimate."
So, you need to download WindowsActivationUpdate.exe using IE only (Firefox won't work because once activated a cookie is needed by IE.)
VIRTUAL WINDOWS XP (500MB)
Install the lot and possibly reinstall the USB driver via the Kies troubleshooter.
Then and only then will this phone be detected. What a palaver.
BTW, it takes about 2 minutes to connect to the phone using Kies and file transfer between Kies and the Galaxy Mini GT-S5570 phone is painfully slow.
Why there is no version of the USB driver or Kies for Windows 7 64 bit and Samsung want to send us back into the wonderful world of XP I have really no idea.