Given A1= 1/5/05 and A2=1/20/05
and range C1:C5 is a list of holiday dates, what can I do to calculate the
duration of the two dates, minus sundays and the holidays?

I've gotten as far as

=A2-A1+1-(COUNTIF(C1:C5,"="&A1)-COUNTIF(C1:C5,""&A2))

A2-A1+1 calculates the duration between the two dates inclusive;
COUNTIF(C1:C5,"="&A1)-COUNTIF(C1:C5,""&A2) calculates the number of
holidays which fall within the dates

I have not figured out a way to count sundays.. anyone with any suggestions?