I'm not a 3D graphics person and never have been so I've been banging my head a little against the wall trying to understand 3D in "Avalon" (WCP now I guess). There's a couple of great articles over here http://blogs.msdn.com/danlehen/archive/2004/07/19/188075.aspx written by a danlehen which really help in making sense of it. Some of it looks similar to the SDK docs but there's a little bit more in the way of example to help you get your head arount it. For me, the piece I was really missing was the idea of "world coordinates". I'd got the idea that we had an origin of 0,0,0 and that's "middle of the screen" rather than "top left of the screen" and that was fine but I was struggling to work out what the dimensions of that space are and the posting helped a lot by saying "Hey, it's infinite in every direction". What a relief! :-)