There is lots of info at deeperblue forums. Chris Gardinal I believe teaches a FII class, and MikeD just got certified to teach the PFI class.
Its all about safety first, and improving depth second. And they really go hand in hand. Polespear and I just took it up a year ago, and we hunt in 50fsw no problem now. You will see your breathholds and bottom times improve significantly with a course.
Be careful pushing your limits like that without a partner by the way.