New installer should work on Vista. If you get the "d3dx9.dll not found" error (or any other kind of D3D error on startup) then run the shortcut in the installation folder.
http://www.unseenstudios.com/evidyon/download/evidyon-setup.msi
Those of you who have already downloaded, replace "c:\Program Files\Evidyon\evidyon.exe" with this file to make your debug logs a LOT smaller and increase the speed of your game:
http://www.unseenstudios.com/evidyon/download/evidyon.exe