As for the AA thing... what I do is render against a screen that is coloured (single colour) close to the actual background of the pic then use AA. That way, the AA blurring (around the edges of the object you want to render) will match up to what it would've been if you had rendered the whole scene in one hit (hope that makes sense). The single colour screen is easy to delete as well, which is why I use a single colour.

Dreams are just nightmares on prozac...
Digital WasteLanD