My understanding has always been that writers *nominate* writers, directors *nominate* directors, etc., but that the whole AMPAS body nominates Best Picture. When it comes to actual voting among the nominees, the whole body votes for every category. The only caveat is that all voters have to certify they've seen the Best Foreign Film and Best Documentary Feature in order to vote in those categories (so I guess they have specific screenings for those you have to sign something or have a receipt showing you attended?).
I'm not absolutely sure of all this. But I do remember there often being talk about the reason the directors of the five Best Picture nominees aren't always the same five directors nominated for Best Director is that only directors can nominate directors, but the whole body of the Academy nominates Best Picture. And I read an article in Entertainment Weekly a week or so before Black Sunday that had interviews with an actor, producer and screenwriter (anonymously), asking them who/what they'd voted for in all the categories and why - that's what leads me to think everyone gets to vote for pretty much all the categories.
Oh, and I thought that once you get *nominated* (i.e., it's not required that you win), you are an honorary member of the Academy.
But you can also be *invited* to be a member (and thus vote) without ever having been nominated - kinda like the National Honor Society in school - you don't have to have any actual merit - you just have to be popular. Grrrrrrr... I read about all this after the Final Blow in March. Yet another reason I'm beyond totally done with them.
