If you have been happily using RawShooter Essentials 2006 with your *ist-
series Pentax and just added or upgraded to a K100D or K110D... you have
found RSE won't load your new PEF raw files.  And the "improved" software
from Pentax is still very slow and clunky by comparison.

The quick fix, if you're a competent PC file mechanic:

1) Open RawShooter.exe with a hex editor (I simply used UltraEdit).
2) Search the file for ASCII *ist; patch whichever *ist model you do NOT
own.  Since I have the DS and the K110D, I zapped the DL model.
3) Starting from the * in *ist, change to K100D or K110D to suit your
camera.
4) Zero out (hex 00) any leftover characters from the former camera name.

DON'T TRY THIS IF YOU DON'T KNOW HOW TO DO THE ABOVE! Also, always
experiment first on a copy of the original .exe file.  

Now my RSE 2006 ver 1.20 build 68 recognizes and processes PEFs from both
my cameras without complaining.  Pentax PhotoLab 3.0 is very lame by
comparison.

RSE, gone but not forgotten.