How do you write a letter of resignation?

Date: 1/26/2009 2:46:21 PM
Author:Sabine
I'm a teacher, and I've already informed our building principals and our superintendent that this will be my last year because my husband is in the Navy and we will be moving to Portsmouth, Va this summer. The principal told me that to make it official, I need to submit a letter of resignation. I asked what exactly it needed to entail, and he said it was really informal, just a letter informing what I had just told them.

I'm struggling a bit on a few things:
1. Who do I address this letter to, and how exactly do I address it? I'm guessing it should just be to the head principal, but how do I word the greeting? Dear? To?

2. How do I close the letter?

3. Do you think it should have the formal letter format (my name and address at the top, etc.) if it's just being put in his mailbox in the office?

Anything else I should remember?

I'm thinking of writing the following:

It is my intent to officially inform you that I will not be returning to teach at x school after the completion of the 2008-2009 school reason. This is due to the fact that my husband's Naval obligation begins in July and will require us to move to Portsmouth, Va. I have sincerely enjoyed working here, and thank you for the opportunity to learn and grow as an educator.

Thanks,
Sabine

What do you think?