Dear so and so,
After much thought and prayful consideration, I find that I must resign my position effective....whenever. I have learned much and gained many friendships during my tenure at blank medical center. I look forward to my new position, but will leave with many cherished memories.
A two week notice may not be acceptable. As professionals, we are often expected to give adequate notice to our employers to allow them to fill our positions (within reason, of course). This may mean that you will be expected to finish out the posted schedule, or whatever the policy is at your institution.
Gentlemen: Please be advised that I have accepted a position at another facility that is more in keeping with my long term career goals and that my last day with___________ will be _______ 2006. I want to thank everyone with whom I have worked for their guidance and assistance, and wish them continued success in their endeavors. Sincerly blah blah blah.
I would not mention future employment (unless you're moving to another state or something similar), especially if you are unhappy with the job you're leaving. Besides the fact that it's none of their business, there are a few whackadoos out there who could make trouble for an employee who is "escaping." If you're on good terms with your manager, chances are you will have told her your plans. If not, why give out information that can be used to make your life difficult.
BTW, ceecel.dee is correct in saying that some facilities ask for more than two weeks notice. Generally, the higher up the food chain you are, the more time they will ask to replace you. Other places will ask that you finish out any time you have already committed to, and that could mean several extra weeks.
This might not seem like a big deal, but it could have a bearing on whether you're listed as eligible for rehire or not. I can hear people saying, "I'd never even consider going back there, so why would I care." You should care because if you're looking for another job several years down the road, prospective employers may check with previous facilities to ask that very question. HR departments tend not to say anything bad in a direct way (due to fear of lawsuits), but telling someone that a former employee is not eligible for rehire stays within the boundaries while still managing to convey a negative report.
For most of us, the two weeks would be sufficient. But it's a good idea to check so you don't inadvertently cause yourself a problem in the future.