Automating the running of a script?

I'm working on a website where one part of the functionality is to sign up to receive a weekly "devotional/inspiritional" via email. Once a user enters their email address, the email will get stored on the server or db (haven't decided which to use yet). Then once a week, or whatever the desired time frame would be, an email would be sent out to everyone on the list.

My question is, how can I automate this to where a script would execute to perform this process?

Thanks,