Zimbio contains a number of sample application letters that you can tailor to your own needs, and alter however you wish. The letters are free, and you do not need to download any files to access the letters - they are right there on the internet. They can be found here: http://www.zimbio.com/Writing+A+Great+Resume/articles/1185/Sample+Application+Letter+Nurses+Applicants.
If these templates do not suit your needs, you can find further examples by typing "application letter for nurse trainee" into the search engine of your choice, or by using the examples given above as inspiration, allowing you to write your own letter from scratch.
- Why do I need an application letter?
In addition, many people overlook the importance of a cover letter, and will either not include one, or will print 20 copies of a generalized application letter out to send to every organization they apply to. But putting in a little extra effort will set you apart from the rest of the applicants.