Calculate sick absence by days per month.

Hi

What I need is a formula (or formulae) that will allow me to calculate how many days of sick absence a person has had in each month given a start date and a return to work date. An added complication is that a person is only classed as being sick-absent on the weekdays that they would normally work (not everybody works the 5 day standard week). What I'm looking at is something like this:

A1 - Date sickness absence began (e.g 10th January 2013)
B1 - Date person returned to work (e.g 13th April 2013)
C2-G2 - an "N" if the person does not normally work that day, blank if they do (where c2=Monday, D2=Tuesday etc)
H2-S2 - these are the cells I want to enter formulae to auto-calculate the number of days the person has had sick that month (H2=Jan, I2=Feb, etc)

So, if a person only normally works Tuesdays, and was sick from 10th January to 13th of April, the formulae should return 3 for January in cell H2 (as there are 3 Tuesdays between 10th January and the end of the month), 4 in cell I2 (February), 4 in cell J2 (March) and 2 in cell K2 (2 Tuesdays between the beginning of April and return to work on April 13th)

I've tried looking at ways to achieve this using NetworkDays(), but can't figure out how to break down the number of days by month. Any help would be hugely appreciated.

Thanks