Triggering a workflow by Date Field.

I have been trying to figure this one out for the past weeks... which I have just got to the point of giving up.
I have a workflow that needs to be started based on a specified date. So naturally this requires a form which I have done... now how do I get it triggered and count down based form the date saved in the form?

Sorry if this is a noob question but hey your workflow and forms are not the simplest to design and use.