Demaestro - 3:36 pm on Jul 16, 2010 (gmt 0)
Assuming you aren't tracking the time that entries are made you want to execute this:
alter table table_name add column date_entered TIMESTAMP;
alter table table_name alter column date_entered set default now();
This way you won't have to update any SQL statements that insert into your tables as this column will default to now() every time a new row is inserted.
Once you have that in place all you do is create a SQL statement that looks for rows with a date > then 7 days ago and < now()