Is there any way to convert v3 poses to work properly with a v4 character?  

Thanks!

There's PuppetMaster (I believe it's at Content Paradise).

But if you have Poser 7 or higher, there's Universal Poses. Here's how you do it:

1. load V3;
2. apply a pose from your V3 pose library;
3. save the pose to another pose library folder (it's best to create a new folder for this). This will automatically save the pose as a Universal Pose;
4. Load V4;
5. Apply the pose you just saved. You'll see that you have two checkmarks in the library: one for the "normal" pose (which only works well for V3), and one for the "universal" pose, which should work - reasonably - well for other characters, including V4.

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So that's how to do it... thanks for the question and the reply!

But can someone explain what difference the Preferences option "Apply Universal Poses" makes to this procedure? Do you have to have this option ticked (checked) for this to work?

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Thanks for the step by step on the universal poses.  It's working reasonably well, and I am only having to tweak little things like the fingers/hands.  Thanks again!!!

Poser 7 comes with a script to batch convert entire folders to "Universal Poses" but I have found more success just applying the poses as is and adjusting it myself.

Poser saves some info about the figure it was made with for a universal pose. It must then recalculate some of the bend angles for the new figure. At least I think thats what happens. I havent found them to be very good if you have hands on thighs for example . 

I just use any pose and tweak the result.