It's a program designed for recent college grads who are applying or who plan to apply to med or grad school in the imminent future. It's a year-long committment that can be extended to two years. The purpose is to give you experience conducting research, and I've heard that you can get a placement even if your prior research experience is limited. You fill out the online application and get 3 rec letters that can be submitted online, and your application goes into a database that different labs can search. So, there's no official acceptance or rejection... you just wait to be contacted by labs (and you can e-mail labs that interest you and see if they have an opening). You should submit your app a few months before you want to start. Some people submit in December/January and are way ahead of the game. I submitted in May when I realized graduation was 5 days away and I had no job. I ended up starting in September.. but I would've had more choices of labs if I'd been in the first wave of applications. You learn alot of lab skills and get to do an independent project... obviously a lot depends on the lab you end up in, but you have the opportunity to meet with various PIs and make a decision. While you're at NIH, they have seminar series and workshops... like recently we had a med school interview workshop and got some pointers from deans at MD, GW, and some other schools. The salary is $23,000. You have to pay taxes, and you can also get health insurance through NIH that your institute pays for. NIH also has a technical IRTA program and NIH Academy, which you can read about on the website
Go to
http://www.training.nih.gov/student/Pre-IRTA/previewpostbac.asp?AppType=Postbac for details.