I hurt my back during Stage 1 doing deadlifts. It is critical that you have good form, especially as you increase your weights. I would recommend watching a lot of videos that detail correct form and then having a trainer at your gym watch you deadlift. You don't necessarily have to hire a personal trainer -- I just asked one of the trainers at my Y who lifts and hangs out in the weight room to watch me deadlift for one set.

You also might want to check out the book "Starting Strength" by Mark Rippetoe -- it gives very detailed instructions on the proper form for all the big lifts.

Edited to add: I think the riskiest part of the deadlift is when you are lowering the weight back to the ground, especially if you are fatigued from your set. Adhere to scrupulous form when you're setting the weight down, and don't increase your weight faster than good form allows.

I injured my intercostals doing deadlifts - recovered now but scared to do them again. Watched vids online to try and get pointers but as far as I can tell I was doing it right although the trainer I have for a class kept pulling me up on form. I plan on asking him to show me again where I am going wrong. Be careful.

One thing that has helped me is switching to sumo deadlifts. If you are tall and long-legged, they might be easier for you to do with good form.