Giving the renderer 4 threads is probably the most efficient choice if you have multiple cores.  Since the Firefly multithreading is rather braindead, it often happens that you have one or more threads finish before the last one finishes - it may not seem too intuitive, but if you have it set to 2 threads, one thread will inevitably finish early, leaving the processor 1/2 idle (one core doing absolutely nothing).

With 4 threads, each thread will be juggled between the two available cores.  It sounds like this will hurt your speed, and in fact it might in some situations, but for general use, you can have 1 or 2 threads complete early and still have the processor 100% busy (both cores).

The little delay you're experiencing when clicking on things might just be that you are running short on available RAM, so as you select things they need to be swapped into RAM so you can work with them.

No patches for poser yet as far as I know.  No opinion of Vista since I don't use it.

Render settings - what does "work well" mean to you?  what problems ar eyou having that are related to rendering?

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