According to Bob  <pfister177@earthlink.net>:

    I don't know the D100, (and don't have access to one), but on
the D70 (2.0 patch level), you select the menu with the wrench icon, and
scroll down to the "Dust ref photo" entry, and then get the following on
your display:

    "Take photo of
    white object
    10cm from
    lens"

follow that instruction, and you are done.

    Note that the "Dust ref photo" appears on the camera's monitor
as a red and white checkerboard, and is not viewable with normal NEF
tools -- except those capable of applying the "Dust ref photo", such as
"Capture 4".

    If your D100 does not have any such menu entry, then it may not
be capable of taking such a photo -- or it may need a firmware upgrade.

    Good Luck,
        DoN.   

Run Capture 4 and ... now here's the important part ... click on the
Help menu item, select Contents, look for Image Adjustment, look for
Image Dust Off. Read what it says.