Meh, several things I've learnt...
You
can change the IP of an interface. ¬___¬ Just learnt it yesterday. "ifconfig nas0 192.168.1.1" to remove the IP conflict I didn't understand when I started all this mess (I kept confusing nas0 with eth0, and eth0 with nas0 in terms of functionality and identity).
Once I removed the conflict, both Ubuntu and Windows partitions are left as server with IP 192.168.0.1 (since I can't change the range used by client Windows DHCP, this I also figured yesterday
).
Client Windows has, as I mentioned, a private dynamic IP. Though this change is not new, it's the first time I do it with the conflict fix and with a static IP on the correct device in Ubuntu partition.
God! What a mess! But, luckily, I've learnt quite a few things with all this.
I'm trying to fix Samba, since the file sharing part got a bit broken with all these changes, but it was Internet sharing what was more important, anyway.
Hope this helps anyone in the future.
While "Googling" for all this, I was led to this thread... 
/ 
