Just built a new system and upgraded to poser pro from poser 4, Q6700 with 4 gig ram and xp pro.
When using four threads the render hangs but eventually does finish, when using one thread it renders in seconds. Should this not be the other way around...

Since you say it renders in seconds using only one thread, this must be with low render settings, or little detail, or a small render, or a combination of those. For such renders, the additional setup time required for using four threads (as explained in the manual) is an unnecessary overhead, and I would expect it to take longer.

But how long is 'eventually'?

All the renders are firefly max settings with same content, v4.2 with high res textures, no backrounds. Single thread about 20 sec, four threads 5 min. Render starts off strong then hangs with barely any cpu activity.

According to previous posts appearing here there is no advantage to using all 4 threads.  Poser is not smart enough to distinguish which thread is in use and to switch off when necessary.

I use Poser 7, not pro. But I DO have a significant push in speed when I render with more than one thread - if the render takes long enough.

If you use multiple threads, the overhead is larger. So if you have a scene which is rendered in seconds, you won't see an advantage in using multiple threads, because starting the render already can take minutes.

If you have a scene with reflections, refractions and/or AO, you will see a difference. If your scenes are big and/or complicated enough for hours of rendertime, you WILL see that rendering in four threads brings an advantage.

Compare it with delivering a sixpack - if you just have to walk for a minute, you are faster without using a car, because starting it and finding a place to park takes more time than just walk over. If you have to deliver it some hundreds of miles away, the car is much faster.

The job defines the tool.

The thing is shortly after install it was rendering with all four cpu's , and was faster than single  thread, which was cool to see the render happening from all over than from just top to bottom. Read some posts about firewalls causing this but not sure what settings to change, using kaspersky  firewall.

I always have poser on its own hard drive and also have to tell zone alarm to let FFrender connect to local zone

Update to slow render. After doing a lot of testing I found that my four core rendering chokes only when using large textures (over 3000 x 3000). With v4 standard textures (2048x 2048) I get high cpu  usage on all 4 cores. Single core rendering with hi res textures works just fine by the way. So maybe it's a video card setting ?