Digital BW, The Print

I now have a Walcom Saphire 4X5 tablet.  While there is a bit of a 
learning curve, it seems to be a marked improvement over a mouse.  I 
do have one question.  While I may have misunderstood the discussion, 
I was under the impression that the pen could be set so that 
increased pressure controlled either brush size or opacity in PS7. 
While pressure controls brush size, I cannot figure out how to set 
the pen to control opacity.  For buring and dodging or erasing part 
of a layer, I would much prefer to have control over opacity than 
over brush size.  Is it possible to set the pen to control opacity?

Thanks to all who aimed me in this direction.  

Steve