As I understand it, CShell is a library of routines that the 3D engine uses to send information through the OS to the hardware. Hardware and DirectX have evolved well beyond the what was around when the game was released, though, and some of the CShell routines don't do what they were intended to in some cases. Also, in one instance, the CShell routine had a bug in it.There is no reason not to try out the revised version. If it doesn't help out on your system then all you have to do is move back a copy of the original.
