Octree or quadtree tutorials in web?

Hi, as in subject, I’m looking for a good tutorial/article about octree or quadtree.

I’ve googled only a few, poor quality.
No books about it in my country :frowning: .

see
http://www.gametutorials.com/gtstore/c-1-test-cat.aspx

nothing free that you know of?

http://www.cs.berkeley.edu/~demmel/cs267/lecture26/lecture26.html#link_3
http://cone3d.gamedev.net/cgi-bin/index.pl?page=tutorials/ogladv/tut3

etc

sorry, it was free some time ago

Thx for links.
About those from gamasutra - worth to register?