Assuming you already have email capability built into the database, one solution I have used for a problem like this in the past is to have a table that stores the date that the notifications were last sent out. Then in the startup form of the database, put in some code that, for instance, says:
If this is Monday, do a lookup of the date table.
If the date in the table is today, then do nothing - the emails have already been sent.
If the date in the table is not today, then send the emails and update the date in the table to today.
That way, the first person that enters the database on a day when the emails are supposed to get sent will trigger the process. You might also want to display a message that the process is ongoing, otherwise the person will think the database is hanging. Also, instead of checking for a particular date, you can check to see if it has been greater than 7 days since the emails have been sent.
If you don't have email capabilities set up, I think the MAPI code to do this through an exchange server is on the forum somewhere.