You need to keep this data in a seperate table, then run an update query at the end of each month. Put a date stamp on each new entry. Have the update query code check to make sure you are not double entering the vacation days by checking the update date month against the current or last month.
Then report on vacation days with another query that totals them all up.
You don't want to have one figure that you are changing every month, like this:
mmcdonal 2 days (DELETE 2 and replace with next value)
mmcdonal 4 days (DELETE 4 and replace with next value)
mmcdonal 6 days (etc)
You want to do this:
April 2005 mmcdonal 2 days
May 2005 mmcdonal 2 days
June 2005 mmcdonal 2 days
Then your query/report/form will show a TOTAL of 6 days.