Possession movie from mid 70's or early 80's, took place at a school, main character was a student that was possessed. The pool at the school caught fire, nails flying at other people, Didn't get to see anymore than that, it scared me a lot as a kid. I have tried forever to figure out what movie it was so I can watch the whole movie.

Think you're looking for a movie called Midnight Offerings... I remember watching it when I was younger - as soon as I read your description it popped up in my mind! Hope this is it - here's a clip showing the nail scene.. Midnight Offerings 7 - YouTube (http://www.youtube.com/watch?v=lfQVFMOzSOY)

Also try The Possessed (http://www.imdb.com/title/tt0076563/)

Dang it! I think the movie I suggested is not the one you're looking for, I just read an in depth review of The Possessed, and that sounds more like what you described - here's a snippet:

I liked how Thorpe was clever enough to matter-of-factly show the fires begin, with no ominous, overripe portents to them (Ford's sleeve igniting before we even realize it is a good example), giving us TV-friendly pay-offs that were still quite nasty (watch the reflection in the window of Ford's body burning away as his arms fold in on themselves, like those self-immolating Buddhist monks). As for the finale, it's beautifully creepy. Hackett, now in full possession by the unnamed Evil, walks through the halls of the school, her make-up a ghastly approximation of her now-corrupt soul, before she takes on Farentino, making unnerving Exorcist-like sounds and squeals and groans, before she spits nails (!)
http://www.dvdtalk.com/reviews/52637/possessed-1977-the/