Perhaps you would be better to create a calcualted column based on the Modified Date of the item. So a create a new column called Expiry, set the type to Date/Time and set that to date only.
In the formula box type:
[Modified]+7
This will give you the expiry date of the content. For example if the Modified Date is 15/10/08 then the expiry date will be 22/10/08.
Apply a filter of
[Expiry] Greater than or Equal [Today]
If you want to not display the content on the seventh day just make the filter Greater Than.
Also if you want Posts to expired based on Creation date instead of the Modified Date, then simply use the Created field.
Ofc the reply 2 above mine is pretty much the same..