To calculate the difference between two dates (in days) excluding weekends using formulas in Business Objects Reporter: see this post.
The best solution would be to handle this on the universe and database side:
If your developer team could implement a calendar table on the database side (and your universe designer makes the appropriate changes such as including the calendar table, joining it properly, creating a universe object “Nbr of days between”, etc.) you could calculate even days between two dates excluding weekends and any company holidays.
Andreas 
(BOB member since 2002-06-20)