counting days from a list of dates

Hi 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)

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.

Thanks

col3: end_date-start_date
col4 : use the networkdays function ( you might need to install the analysis toolpack for this one)