Wolf3D is like Doom, but it is only on two planes. You cannot walk up and down stairs, nor can you do any real polygons. It's just Sprites moving around, shrinking and ballooning, with walls. It's hard to explain, so look for a Wolfenstein 3D demo floating around the internet. Run it in DOS, though; it hates Windows 98. And if it hates that, I don't know what it'll do on an NT-Based OS like Windows XP.

-ThO (Violet needs to make a Crysilis. Now. Or else sasdf)