Texture Mapping is basically a 3d to 2d conversion. Say you have a polygon with three points, you have a texture with three points on it (different points), you interpolate between the points on the screen and the points on the texture, and presto, you have a texture mapped polygon.

check out Perspective corrected texture mapping

Michael Abrash's books show you how to do texture mapping, but thats not REALLY necessary, cause you could just use Direct X in Windows.