Count Number Days Excluding Weekends

I am trying to set up a sick leave list which will work out the cumulative total for the last 12 months (from last day of last sick entry). The problem I have, as the is is added to, I need a function/formula to work out 12 months from last date and then add up the no. of sick days from then to the last date. Hope this is clear. The next problem is I need it to work out total days and then without weekends. Below is the chart I have to work out.

Column 1 Start date of sickness
column 2 End date
Column 3 the number of days sick in period (column 2 less column 1 in days)
column 4 the number of days sick in period above excluding week ends (column
2 less column 1, less weekends in days)
column 5 total sick days in last 12 months from date in column 2 going back
a year including weekends
column 6 total sick days in last 12 months from date in column 2 going back
a year excluding weekends

What function or formulas can I use to calculate column 3,4,5 & 6. I am a not very experienecd in Excel