isn't there a clear line between creationism, ID'ism, theistic evolutionism?
Not really; they sort of overlap.
Creationism is usually used for those who believe in the Biblical creation story. Young Earth Creationism teaches that the earth was created by God approx. 6,000 years ago, in six 24-hour days.* Old Earth Creationism (OEC) looks at the word for "day" in the Bible and notes that the same word is used elsewhere for "period of time", thus the 6 "days" are taken to mean 6 divisions of time which could each be millions of years long. Some OEC proponents believe the earth is old, but life is young; others believe God created life over the course of the earth's long history.
The main difference between OEC and Theistic Evolution, as I can see, is that OEC says God created the various species uniquely, while Theistic Evolution says the species evolved but that this does not mean God was not involved. Although, even in Theistic Evolution there are differing points of view as to how involved God was. Some say He actively guided the process of evolution (thus, it is not "random"), others say it *is* a random process, but that God, in his infinite wisdom, is the creator of the process itself, and knew in advance what the end result would be. Either way, theistic evolution believes that evolution is the tool God used to create mankind.
ID differs from creationism in that ID does not insist on God as the creator, and ID allows for (but does not insist on) the existence of macroevolution.
ID differs from theistic evolution in that ID does not insist on God as the creator, and ID allows for (but does not insist on) the absense of macroevolution.
ID differs from what I'll call "Darwinian evolution" in that ID does not insist on (although it does allow for) the existence of macroevolution, and, more specifically, ID states that at there are some features of life which appear to have been designed. Well, actually, Evolutionists readily admit that life "appears" to have been designed. Francis Crick is famous for saying, "Biologists must constantly keep in mind that what they see was not designed, but rather evolved." Entire books have been written by evolutionists explaining why evolution is an adequate explanation for the appearance of design in life, and entire books have been written by ID proponents explaining why evolution is totally inadequate.
Sorry for the long post.
I was a Biology major in college, and I have always found this a fascinating subject!
*edited to add (after reading Terry's posts, below) that not all YEC believers say the earth is 6,000 old, but all say it is relatively young.
