Query arising from Tutorial 10.

Hello all, I have been slowly going through the tutorials at the NeHe site and I have a query that I am hoping some of you who have much greater knowledge of OpenGl can help me with. My query concerns Tutorial 10, the infamous Tutorial 10. While the tutorial is very comprehensive, well it is for me anyway, and the program works pretty well, I was a bit dismayed when I found out that the program allows you to walk right through the walls. It is probably because it is a more avdanced subject. So I had a quick look on the NeHe site for a more advanced version of this tutorial, that is, one that would stop you walking through the walls but I could not find one. I probably just overlooked it. So my query is this, is there a more advanced tutorial of tutorial 10 at the NeHe website? If there isn''t one, where would a find a tutorial with the source included discussing making a more advanced 3D engine, that is, one that doesn''t allow you to walk through walls? Thankyou and regards, Vaughan MacEgan - celtic@allstate.net.au