I want to use dynamic hair for a character who is upside down.  Let's take Crinkly Hair for V4 by KaiZ (because growing the hair gives my conpitions.  I need to conquer that, but later).  OK, I have V4 Upside down.  I load the hair.  I open the hair room  and now what?

Unless it's a dynamic hair prop the hair room won't do anything for you there, as far as I know.

The hair involved is a dynamic hair prop, actually.

Hmm, ok. Did you try re-calcing the simulation? The gravity settings should have some effect I would think.

OK, let me rephrase the question...  What gravity settings do I need to have dynamic hair affected when the figure is upside down?

The dynamic hair I used came with a default setting and i used that.
In one case the gravity was -0.0006  and Position Force 0 . This worked well because it was a simple pony tail and didnt need to keep a style, the gravity determined where the hair goes.
However if you want to keep a hair style you need to set position force non zero or the gravity will make it all straight (I have an example with gravity -0.0006 and position 1).
Also:
-If the hair will come in contact with body parts, dont forget to set collisions on (for the body parts too).
-If you want to make quick tests, reduce the hair density. It will not look as nice in a render, but you can do more experimentaion and once the general effect is OK increase the density back

Hope this helps.

showing my ignorance, but what happens if you rotate it on the 'y' axis by 180 degrees?

Pakled,
How do you mean? If you mean you have a figure with dyn hair on in frame 1,and you pose  the person(with hair)  in frame 18 rotated by 180 around y and run a simulation of 36 frames,
the figure will rotate 10 deg every frame. the top of the hair will move with head but the bottom edge will lag behind like in reallife . so it will look twisted. after step 18 the figure stops rotating but the hair will continue to turn till it catches up with the head.
Not sure if this helped. I (or anyone else ) could post a picture if that would help

I love the results of dynamic cloths and dyb hair. Like condensing an animation into one still pic.
Shame its computer resources intensive.

PS - The first step to wisdom is recognizing you're ignorance... so well done!