IMHO, there is a huge difference using the 64bit version of Carrara. Howie's scenes seem to be much happier. Howies scenes are pretty resource intensive, and as I recall, you had to be farily careful with what you did to keep under the RAM limits in a 32 bit environment (but my memory could be wrong).

I've done some projects where Carrara was consuming over 12Gb of RAM, that's not something that you can do with the 32bit version. Carrar Pro 8.5 has been quite stable for me, others may have different experiences.

HDRI stands for High Dynamic Range Image. HDRI's can be used just for lighting, just for a background environmenet, or for both. It's basically the same as IBL in Poser. Basically, light intensity (the brightness of each pixel) information in the HDR Image is translated to a light source in Carrara. So if there is sunlight in an image, it will typically be the brightest light source in your scene. I really like the soft lighting you get with HDRI. They are also great to provide something for reflective materials to reflect. I used an HDRI both for base lighting and for reflections in this image: http://www.renderosity.com/mod/gallery/index.php?image_id=2130745

Hope this helps!

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