A while back I read a fic based on the premise that Spike beat Buffy in school hard, used her to heal Dru, and then turned her.

A couple other main characters were turned as well if I remember correctly. It was like 3 different "books" and the story leaves sunnydale and goes more into the lives of soulless vampires rather than the tamed ones we normally read here.

Anyone know where I can find it?

--Jen

Based on the thin information you provided, this sounds a little bit like Kantarya's unfinished series. . . The Crimson Codex.  You can find it all here:
http://kantayra.under-my-umbrella.org/browse.php?type=categories&id=2&offset=25