Here is a function that does just that.  You will need a holiday table that
has each holiday in it.  You can create one with the names in the code or if
you choose to use different names, change the code:

'---------------------------------------------------------------------------------------
' Procedure : CalcWorkDays
' DateTime  : 5/8/2006 16:34
' Author    : Dave Hargis
' Purpose   : Counts the number of days between two dates excluding Saturdays,
'           : Sundays, and any days in the Holidays table
'---------------------------------------------------------------------------------------
'
Function CalcWorkDays(dtmStart As Date, dtmEnd As Date) As Integer

   On Error GoTo CalcWorkDays_Error

'Calculates the number of days between the dates
'Add one so all days are included
   CalcWorkDays = DateDiff("d", dtmStart, dtmEnd) - _
       (DateDiff("ww", dtmStart, dtmEnd, 7) + _
       DateDiff("ww", dtmStart, dtmEnd, 1)) + 1
'Subtract the Holidays
   CalcWorkDays = CalcWorkDays - DCount("*", "holidays", "[holdate] between
#" _
       & dtmStart & "# And #" & dtmEnd & "#")

CalcWorkDays_Exit:

   On Error Resume Next
   Exit Function

CalcWorkDays_Error:

   MsgBox "Error " & Err.Number & " (" & Err.Description & _
       ") in procedure CalcWorkDays of Module modDateFunctions"
   GoTo CalcWorkDays_Exit
       
End Function