I have a couple of quick notes:

1) NASM is required too
2) The tempfile code in sbt86.py’s disasm() doesn’t work under windows, as the file is locked (I worked around it by not auto-deleting the temp files, and closing before the ndisasm call)
3) You need to run make once in the libnds directory before trying to build RO, and probably do a ‘make nds-release’ in the libfat dir too

Of course, I’m asking for trouble trying to build this under Windows