Here's some more food for thought, Lyne:

Sometimes with AA, it's better to go with a low-quality setting and render your image at twice your intended size. When you re-size it in an image editor after the fact, the AA will automatically look nice and pretty. Obviously this may not work with the HF scene because of its size, but it's a nice trick to know and can actually give you better results in less time in some instances.

Now that you've switched to Carrara, you'll need to start thinking like a professional. (Poser and DS are more for the hobbyists) One big rookie mistake that we've all made is to create scenes that are beyond what our hardware can handle. Pros from ILM to Pixar almost always break larger scenes up into smaller, more manageable pieces and composite everything together in post. For example, the atmosphere, the terrain, the vegetation, and the character(s) could all be separate layers. Going this route gives you the option of using lower-quality render settings on the background layers where the viewer won't notice the difference, and cranking up the quality for the characters where you may want lots of detail. This requires a lot of planning in terms of establishing a working pipeline, but once you get the hang of it, there won't be anything you can't handle!

JT