Users delete their own membership

[Marv]

For month now I´m looking for this one, too.
For security reasons it should be an option which has to be confirmed by a link in an email (similar to the confirmation of the registration process).
If a user decides to end his membership his/her user status should change to "guest" and all posts should remain in the forums.

Anyone out there who could spent some time on that ? Would be really appreciated !