Resignation Pro

What is the best way to structure my resignation letter *m*...?

I work for a University and will be leaving one department to work for another - technically, I'm not resigning from the University, however, departments here are distinctly different entities of the University. How should I word my "resignation" letter to my department without saying resignation (and without giving them too much personal information on where I'm transferring to)?

Public Comments

1. Resignation Letter Samples: http://jobsearch.about.com/od/resignationletters/a/resignationlet.htm