OK, I found the v10 drivers here and this enabled Windows 8 to recognise the Smartboard using Trigster79's method.
I also got the board to work using the old serial cable connected via a female-to-female gender changer and a Prolific USB-Serial cable. The power needs to be connected via the PS2 keyboard connector and a USB adapter. Messy (and uses 2xUSB ports), but might help if you've only got the old serial cable.