Count days per month within a period

Hello everyone,
I have the following problem:

I have a cell with a start date and a cell with an end date.
Then I have some columns with many different months, eg. May 2010, June 2010 and so on. Is there a way, that Excel just counts the days of the respective months within the given period?

What, if the start date is the same as the end date?

Thanks a lot in advance and

kind regards.