Two solutions found online, two problems.

1) =NETWORKDAYS function should do the job, but I keep winding up with a
#NAME? error. (Using Excel 2003)

2) Formula suggestion, where A2 contains the earlier date and B2 contains
the later date:
=MAX(WEEKDAY(B2,2)-WEEKDAY(A2,2),0)+1+INT((B2-A2)/7)*5
gets hosed when one or both days are Saturday or Sunday
http://www.ozgrid.com/forum/showthread.php?t=65032

An explanation for 1), modification of 2) or other suggestion is
appreciated. TIA.