Rather than programming (which refers to using visual basic to manipulate the
sheet) your request can be handled by using conditional formatting. You
didn't mention whether you are using 2007 or 2003; I'll provide 2003
instructions here and you can adapt them to 2007 if needed.
Select the first cell (C1 or C2, depending on whether you have a header row)
and apply conditional formatting (I'll use C2 as my sample):
more than 90 days in the future:
(cell value)(is greater than) =now()+90
or if you want more than 90 days in the past,
(cell value)(is less than) =now()-90
then select the appropriate formatting (for example, format/pattern/red to
make those cells red)
use the paintbrush tool to paste that formatting across your whole range. If
you want to avoid making blank cells (at the bottom of your range) appear
highlighted, then use conditional formatting a slightly different way;
(formula is) =AND(C2<>"", C2 <(now()-90))
HTH,
Keith