Excel 2007 : Autofill date

[sublimemovement]

I hope I am posting this in the right section.

Well I am using excel 2007 and I am trying to get a cell to auto fill the date in this or a similar format:
dd/mm/yyyy - dd/mm/yyyy

The time span I am looking for is a week from Sunday to Saturday.

Ultimately I would like the first date to be the nearest Sunday preceding the date the workbook is opened and the second date to be a week out.

I need this to be done in 1 cell

Thanks for any help in advance.