Mobipocket DRM works fine with a linux PC. Devices which use mobipocket DRM have a PID that you can read directly on the device, then you communicate this PID to the stores on which you buy books. No need of windows anywhere in the process.
Back to epub format. I've seen indeed people mention that they can use adobe digital editions with wine under linux. I had trouble doing that in the past, but I just succeeded!
coredump, in case you want to try it, the link to download the installer for digital editions is:
and you can find free drm'ed books on board, look on the 'help' link on the left of their home page (I _think_ the book is epub but I'm not sure, but since it opens with digital edition it should be the same kind of drm). When you download the book, only a small file is provided, called 'URLLink.acsm'. Save it and then drag and drop it in digital editions.
EDIT: Turns out the file you can get at books on board is a pdf. It would be nice to be able to find a free drm'ed epub for testing.