Resigning after Workers Comp Leave

I'm looking for advice. I have been on Worker's Comp leave after a serious attack from a patient. I have just received clearance to return to my current job. During this time, a position opened up at a hospital within the same medical center in an ER I've been really wanting to work in for quite some time. I applied, interviewed, and was offered the job. Since I'm about 100% sure I am going to take the job I'm trying to figure out how to properly resign.
I will probably be back to work within 7-10 days after all my paperwork clears. Should I mail my manager the letter now, before I'm back, or should I give it to him my first day back on the job? Which would be proper? And if I send it now, should I include 2 weeks notice AFTER my start date back, or two weeks from the date on the letter? Or longer??
If it were me, I would send the letter now and let them know you aren't coming back. They are probably wondering if you really are coming back if its been a long time. But thats my .
This is a good time to let them know that you won't be back, because they have had to fill your spot in the schedule for the time that you've been off, so it would be easier for them to go on like they have been than to anticipate you returning and counting on you for the next schedule.
I would just send them a letter stating you will not be back, resignation effective date of expected return.