Buying rights to songs?

Hey,

So, I was just sent a notification by facebook that one of my videos contained a copyright violation. Go figure, it was 8 seconds past that magical 30 second mark. Anyways, I'm wondering what I have to do to get the rights to music to use it in a DVD that's going to be distributed freely. After that little thing, I've become paranoid about the matter.

We met some people at Brostock who were talking about people who make snowboard videos, and how most of them (which showed at an extreme sports video film festival in NC or something), didn't license their music. They stated that as long as profits didn't make it over the 5000 dollar mark, that they wouldn't be sued. I thought this info was dubious at best and am wondering if there is any truth to it. I'm assuming that what they meant is that unless there is a 5000 dollar or more profit, it wasn't really worth it for them to sue or something...