Calculate hours difference excl weekends

Hi, I hope someone can help with this
I have 2 date fields
A1 is: Nov 2 2012 12:57PM
B1 is: Nov 6 2012 12:08PM

How can I easiest calculate the numbers of total hours passed between these 2 fields

thanks

=CONVERT(B1-A1;"day";"hr")

Hi DubX

Try: =B1-A1 & Format cell as [h]:mm

Thanks, tried both and doesn't work.
I think the problem is that the excel file I recieve has not these cells formatted as date just general so excel can't recognize what is actually in the cells.
Even if I format the cells as date mmm/dd/yyyy hh:ss does not work for some reason