You definitely need to get used to looking at the computer screen for an hour at a time and doing questions in that format. But I gues there are other sources besides Qbank.
A FREE CD that you need is the Sample Items that the NBME puts out. You should be able to get this either from your school or request it from NBME's website. It's only 180 questions for each step, but great to do in the last couple days before the test. Several of the questions on my real test were very closely related to topics they tested on the CD. They weren't exact replicas, but they were testing the same idea. Kaplan has detailed explainations to these sample items on their website for free.
ALWAYS READ THROUGH THE ANSWERS WHEN YOU DO QUESTIONS - you aren't testing to see your score so much as to learn from them how to answer correctly on those topics.