AFAIK, to kill netbios completely you'll need to add the following lines to /etc/smb.conf.
disable netbios = yes
smb ports = 445
You'll also need to stop nmbd from starting. You can do that with the following command:
sudo launchctl unload -w /System/Library/LaunchDaemons/nmbd.plist
Doing this will probably break name resolution of windows clients via netbios (of course). It may also break browsing windows networks.