ITH stands for "Interactive Text Hooker". AGTH is an equivalent (Anime Game Text Hooker).
You should find if you do a quick Google search. I downloaded most of what I needed with links on Hongfire.com if I recall correctly (should be one of the first link on your search). It's been a year now since I installed everything, so I don't remember all the process. I would have to go back into all my files.
Is there a particular game you would like to play?