Digital BW, The Print

At times, I notice posterization -- a very grainy look -- typically 
in areas of sky when the image is scanned.  For example, I scanned an 
image with a large area of gray, cloudy sky where the posterization 
(or break-up) was obvious in the pre-scan.  I use a Nikon LS 2000, 
scanning at 12 bits (16 in PS) and in this instance the film was 
Ilford HP-5.  While I know there are a number of techniques to deal 
with posterization in PS, I wonder if anyone has some ideas about how 
to minimize it when scanning.  When I scan I usually set the white 
and balck points and, at times, use a curve adjustment.  My scanning 
objective is to bring as much information into PS as is possible 
rather than produce an ideal image.  Is this just a function of the 
digital process that has to be dealt with after the fact, or is there 
something that can be done to avoid it in the first place?

Let me add that I joined this group in September and converted my 
1200 to MIS-VM inks shortly thereafter.  I have learned a tremendous 
amount from all of you in a very short time and I want to than 
everyone for their generousity.

Steve