Is there a ruler or something akin to that in Poser7?  What I'm trying to do is have the light (=<) shine on "A", but then stop at "B" so it doesn't hit the wall at "C", below.

=< - - - A - - - - B - - - - C

I'm trying to use the "dist end" dial, but that makes the light start to fade at B so it's just dimmer at C. If I shorten the "dist end" value, then it just starts dimming at A.  I want to get it to stop dead at point B so it doesn't hit point C but will hit A at full intensity.  Will getting the exact distance from the light to "B" and putting that into the "dist end" make that happen?

And a^2 + b^2 = c^2!

In this picture, preview is on left and render is on right.  The ball is 'B'
and the wall on right is 'C'.

Try this tut by Dr Geep:
www.drgeep.com/p4/l1/l1.htm
it's about "dist end" and "dist start". BTW you can find there MANY other tutorials (not only lights).

Another hint: if your scene is complicated, use primitives like these
for quick testing, then copy the light parameters and apply them
to the light in your real scene.

Ah.....DrGeep.com = fantastic.  Thanks!