Finally got it to work after...
I went from Vista home premium 32 bit to Win7 64 bit because that came with the replacement laptop.
The DWA 160 USB dual band adapter wouldn't work at all on the new system.
Installing from the CD went just so far and then said it couldn't detect the adapter.
Downloaded the latest drivers.
Still couldn't detect it.
Turned off Windows automatically installing drivers.
Plugged in the adapter.
Browsed for the driver and pointed to the folder containing the Vista-64 drivers for it.
Tried again with the XP-64 bit drivers.
Success this time.
Remembered to turn automatic driver installation back on for the next new device.
But should I really have had to do all this?
And would a less experienced user have known what to do and how to do it?
There are three revisions of the DWA 160, two with Atheros drivers and one with Ralink. Turns out there is only development and maintenance on the Ralink, D-Link aren't maintaining the drivers for the Atheros version any more.
There is no way to tell which revision from the box until you open it, and the Atheros versions are still on store shelves.
More unethical behaviour from the manufacturers.