From this article I have learnt, that DWM is enabled only with AERO:
Let’s recall: without Aero turned on, the DWM is deactivated, so there’s also no more 2D acceleration, either (this applies equally to Windows 7 as it does to Vista)
What is the easiest way to tell whether AERO / DWM on Win 7 is enabled / disabled? With some themes it is (visually) obvious, but with some others not (especially not when using remote access like VNC).
Is there some dialog where I can see that AERO / DWM is enabled / disabled?