No, not a matching range of handbags and accessories.....

My Poser 7 seems to always use relative co-ordinates for each object/figure.  Is there any way to force it to use absolute co-ordinates so the rotation axes remain constant?

In most 3D apps, coordinate systems are relative to the parent.  If there is no parent, then they are global (absolute).  For figure body parts, it would make no sense to use global coordinates as you are rotating about the parent system (always!).  Global rotations would be meaningless in this case, if not destructive, to the process as you would be rotating about the world origin and not the parent system.  Nonetheless, in C4D for instance, you can work with either system.

For parented figures/props, the only recourse in Poser is to unparent to the Universe, do your transforms in that system, and then reparent.  It must also be realized that the default local coordinate system is affected by the object's origin and orientation.  If a prop has a non-zero orientation, its system will still not coincide with the world system.

As Kuroyume says, there's no good reason to have absolute rotation on
a 'realistic' figure.  The limits on real bones and muscles are always relative to 
the nearest connected part of the body.

I can imagine a couple of special cases where you might need to sense and
control each angle in absolute terms: maybe a planetary system, or
a robot arm that moves things within its own small 'world' while the whole
'world' is riding on a larger conveyor belt.
 
Is that the type of setup you're considering?