Zune DRM? .NET DRM? Silverlight DRM? Windows Media DRM?

Which one? You're being awful vague. Just to settle your curiosity, we just had to create a Silverlight based kiosk, thus .NET and we had to do research into their Offline DRM. It meant that it wouldn't fail if our app couldn't get online.

The DRM was for the embedded videos, the actual install of the app - wouldn't install if it did not have access to licensing server - think certificate authority - and despite having the ability to synchronize from a central server, at times, we had to compensate for occasional downtime, so we use the aforesaid offline DRM.

Do the research. We had to. It's there. And if you're unwilling, that's on you.

Zune, Media Play for Sure, even signed apps for the Vista/Win 7 Widgets have a DRM routine. Third party apps and frameworks exist for that too - Active(something) was another route to do so... but it was cost prohibitive and we couldn't use their servers to manage installs from what I remember.

That's a start... enjoy the research.