Thank you ChronoGrl.
I have actually never heard of Black Christmas, but I'll get hold of a copy as soon as possible. Regarding Ils and Ilside, I've never been able to track these down. I don't think there's any nordic releases for these. But I should have no problem finding it on a british site
I think i'll go with your idea. Start out with Psycho, try to check out Black Christmas as a "mid stop" before wrapping the paper up with a modern one. I've heard great things about both Ils and Inside, so these might be the way to go.
I just hope I'll be able to pinpoint the differences in these movies and explain the evolution of the genre.
Edit: Just to be sure, this is the Black Christmas you're talking about?
http://www.imdb.com/title/tt0071222/