The "flash" source code from GitHub is directly compatible with 32 bit XP - provided you don't try to compile it using a Microsoft compiler as it uses C-99 extensions. I've just compiled it without any trouble on XP using gcc from the MinGW distribution . The USB driver is already available in XP - you just need the same inf file as works in Windows 7, ie EFM32-Cdc.inf. The XP build is reading the UID and firmware CRC and uploading new firmware and runs on 64-bit Windows 7 as well.
The configuration software is more tricky but I've managed to edit main.c and hid.c so that usbhidtool will compile in MSVC 6 and it's now working perfectly from the command line in XP. My grasp of C is very shaky and it's a long time since I used Visual Basic so it may take me some time to produce a working user interface - although I have progressed as far as setting the AudioMoth time in either UTC or local time.