DateDiff in Access Excluding weekends

Hi there, I?m using Access 2000 and want to calculate the difference between two dates in hours. I have two fields in a form [DateReferred] and [DateCompleted], both as long dates and stored in a table. I need to display a result in the same form as [Referral time] (hours). Sounds easy, but I also need to exclude Saturdays and Sundays, and ideally need to exclude hours outside of work (work being 9am to 5pm). I?m trying to do this as a public function (VBA) but having trouble even returning values to the form at present, please help.. KS