How do you calculate the hours between two dates excluding the weekends?

Hi, how do you calculate the hours between two dates excluding the weekends?

A1: 06/06/2013 12:00 AM

B1: 06/12/2013 12:00 AM

I get 144:00 as difference using the formula =IF(B1="","",(B1-A1))

However June 8 and June 9 are weekends here in our place, so the result needs to be 96:00