macro to lookup two dates and return figure in corresponding month columns

Hi,
Please see attached my example. I am looking for a macro which will lookup up my start and end dates (columns B & C) and add the allocation figure (Column D) to the corresponding month columns (Column F +).
For example, if my start date is: 01DEC13 and end date is: 31JAN14 and my allocation = 0.5, then I would like the macro to populate the month columns of Dec-13 and Jan-14 only with 0.5

My month columns will go out until Dec-2016

Thanks

Jen