Unfortunately I can't test it in Vista, so I can't be of help any further to you, but I recommend you to try EVR rendering mode (CTRL+P -> Video -> Video rendering)
DirectShow is not a codec, is a set of APIs made available from Microsoft in their DirectX to allow programmers to do video rendering manipulation.. (achieve their application to render something to video)
Ok, mine is a really bad explanation, for better references:
Good reading