Filling in a Date Series using the Fill | Series menu command

Using the Fill | Series dialog box, I want to fill in a series of dates, by
month, where I know the beginning date, the end date, and the number of
months. The 'Stop Value' box is only allowing me to enter a date string
(e.g. '12/31/2005'). Instead, I want to enter in a cell reference, to a cell
that has the end date. Is there a way, or a way to write a macro that will
fill in the series, referencing begin dates and end dates contained in other
cells?