Look at data validation in XL Help.

For instance, with A1 active, choose Data/Validation and enter


Allow: Custom
Formula: =WEEKDAY(A1,2)<=5

In article ,
grobertson wrote:

Hi,
I have a work sheet that cell A1 requires you to enter a date in the
following format DD/MM/YYYY.
What I would like is if a date is entered into that cell that is not a
working day (i.e. Weekend or Bank Holiday) then I would like excel to either
display an error message or make some sort of error sound.....
Is this possible?
Many Thanks,
Glenn Robertson