Finally got it working. XP just needed the driver usbser.sys in system32\drivers which is the %12% path in the .inf On Win8 it just started working without doing anything(!) The only other issue I had was that I had to use a 2-digit COM port (Win8 had assigned a 4-digit port). Further discussion on these issues can be found on the developer forum at :
https://www.mobileread.com/forums/sho....php?p=2444409
http://www.mobileread.mobi/forums/sh...173792&page=12
Cheers!