Gulikoza has found a neat tool to help people play the DVD version of Wing Commander 4 on modern systems. His basic Dxmci patch is critical to getting the game running without the hardware decoder board it originally shipped with, but users of some programs like PowerDVD occasionally run into conflicts. The merit patch allows players to prioritize filters and play without uninstalling other software. You can learn all about getting WC4 DVD to work at Gulikoza's website.
Now if you install mpeg2dec and assign it a high merit, it should always be loaded instead of WinDVD/PowerDVD filters. You can leave PowerDVD installed (it will still function, since it loads filter directly, not by merit).