You cannot use dx6 on windows xp. The reason you get different reports when running dxdiag on the c: drive and on the CD is for the simple reason that on the C drive it checks the files on the c: drive (your system files) and on the D: drive it checks the files on the CD (the ones that come with SMAC).
What you need to do first is download dx 8.1 and reinstall it. It can be gotten from
www.microsoft.com/directx .
Second if you have a pentium 4 you need to change ForceOldVoxelAlgorithm=0 to ForceOldVoxelAlgorithm=1.
Try to start the game activating terran.exe (smac) or terranx.exe (smacx) rather than axstart.exe (the splash screen). Some people have trouble with the splash screen but the games actually run fine.
If its not solved by now you need to isolate which component is making troubles. It is typically the graphics component or sound.
A simple way to check the sound system is to rename sound.dll and soundx.dll to something else (the game will now have no sound). If it runs know you know its the sound system that is making troubles.
A simple way that will (almost) always detect graphics problems is a) set your resolution to 800x600 x 256 colors b) set hardware acceleration to None (both are done in display settings in control panel - acceleration is under advanced --> trouble shooting.
If its graphics, its your driver almost certainly. Nvidia update their drivers extremely frequently and the reason is usually to improve the speed when using more than 28 lightsources in "Final shootout 6½" or to eek out three extra frames per sec. in "Alien blaster pro". Not infrequently this improved performance is done by sacrificing some compatibility.
Try with a model 3-4 generations back or use the one built into winXP.
Anyway once you know which component is making the troubles you can take it from there.
