go to DataValidation and select custom and type the following formula:-

=OR(AND(C3$G$1,C3<$G$2),C3="tbd")
where cells G1 and G2 house the dates (may be the upper and lower limit)

"Jim Johnson" wrote in message
...
Is there a way to create a validation rule that is used 90% of the time
and
also to specify an exception for the other 10%? If I had a field that was
intended to display a date and set up my validation for the date, could I
then create an exception that would allow me to type "tbd" for those dates
that have yet to be determined?