I just run some CPU utilisation stats while doing a Poser render.

I outputted utilisation percentage of all the 8 processor threads of a 4-processor system once every second and examined them. Interesting results.

When using Poser7 in a "separate process, 4 threads" state, 4 processor threads were used leaving 4 idling, but the used threads were showing 90%-100% utilisation level.   

When using Poser7 in  only a "4 threads" state, up to 8 of the 8 processor threads (all 4 cores) were used at all times, but at significantly lower utilisation levels per thread (between 30% to 90%). And at almost every interval 1-2 threads were not utilised at all. I suspect the rendering I did was not giving enough of punch to use all the threads.

When using Poser7 in only a "2 threads" state, up to 4 of the 8 processor threads were used at all times (2 cores), but again at lower utilisation levels per thread.

When using Poser7 in only a "1 thread" mode, up to 2 of the 8 processor threads were used at all times (1 core), but again at lower utilisation level per thread (again between 30% to 90%).

Conclusion: since "1 thread" mode actually seems to use 1 processor core (both threads in it) and "2 thread" mode actually seems to use 2 processor cores (4 threads), it leads me to believe that Poser can actually use all the 8 threads that are available. "Threads" in the Poser general preferences therefore apparently means rather "cores" and it is up to the OS to deploy the work at hand at maximum efficiency.

This was just a rough test that outputted thread utilisation on 1 second intervals. On the other hand the maximum thread utilisation when "doing nothing" is at maximum 3% of up to 2 threads at the same time (mouse movement etc.) so I'm fairly certain that all the levels I saw were caused by Poser render and that only.