Network Days Calculation

[macdca]

I want to subtract 2 dates in columns A and B into a new column M, that takes into acount network days.

<TABLE style="WIDTH: 162pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=216 border=0 x:str><COLGROUP><COL style="WIDTH: 81pt; mso-width-source: userset; mso-width-alt: 3949" width=108><COL style="WIDTH: 81pt; mso-width-source: userset; mso-width-alt: 3949" width=108><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD class=xl22 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; WIDTH: 81pt; BORDER-BOTTOM: #e0dfe3; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" align=right width=108 height=17 x:num="40555.394189814811">A 12/01/2011 09:27</TD><TD class=xl22 style="BORDER-RIGHT: #e0dfe3; BORDER-TOP: #e0dfe3; BORDER-LEFT: #e0dfe3; WIDTH: 81pt; BORDER-BOTTOM: #e0dfe3; BACKGROUND-COLOR: transparent" align=right width=108 x:num="40557.708106550926">B 14/01/2011 16:59</TD></TR></TBODY></TABLE>

So I would like to calculate the difference in days, hours and minutes between the 2 dates above for example but only showing work days only?

I know the number of network days between the date columns using the usual function. But I have a custom format dd hh:mm for the calculated column M and network days column cannot be subtracted from this. has anyone got a better idea of how I can do ths?

Thanks