To me, that's a mess to deal with and the support calls saying why their game is running slow.
MSOGL - this is an implementation of OpenGL 1.4 that uses Direct3D under the covers to hardware accellerate the application.
Legacy ICD's - These are the ICD's that are available today for use on Windows XP. These will continue to work on Windows Vista, but will disable the DWM when they are loaded in to the process of the application that's using OpenGL. The reason for this is that Legacy ICD's operate directly on the GPU without going through Windows at all, and we have no way of redirecting application's output in a stable, predictable manner.
Windows Vista ICD's - this is a new path for 3rd party ICD's introduced for Windows Vista that will work in a way that is compatible with desktop composition. Essentially allowing direct access to the GPU for hardware accellaration, but then having the final surface that appears to be the front buffer to the application actually be a shared surface that gets composed by the DWM