Email notification to user prior to password expire

Hi All

I have a requirement wherein I need to send a mail to all users to change their password 2 days before it expires. I found that in table URS02 , field PWDCHGDATE gives the last date when password was changed..Can anybody help me to build further logic so that the users will get mail 7 days prior to expiry date of their password, say 30 days is my password validity.

If anybody has worked on this kind of requirement , pls give your inputs on same..

Regards

Babita