How to send an email to the node author when a date is approaching? The user has created a node and has set a future date to be alerted of the approach of this date.

I want the user receive an email when the set date is approaching.

Making the user able to change the approaching time would be great.
Any sugestions?
Have you tested Rules, this is the module to do such actions based on events.
Here is a tutorial to help you with this: Publish content based on a CCK date field.

Also don't forget to enable the debugging feature of rules under admin/rules/settings.