The .mos editor needs
- .NET framework (doesn't have to be 1.1, I've just installed 2.0 runtime on my own rig)
- DirectX 9
- Managed DirectX (if not already installed with DirectX 9)
which should be installed in that order.
Vista uses DirectX 10 which has entirely abandoned Managed DirectX. So you could try installing DirectX 9 from the Windows Update site. AFAIK it doesn't replace DX10, just adds in components it doesn't have but DX9 does. Then run
mdxredist.msi (the patch on Korean Skies) to make sure.
While on the subject of the MOS file editor, does anyone know of a tut on the use thereof? I have the better version from the Terrain SDK (thanks for the tip, Mathias) but the documentation is terse as usual.