You can use Roku's built in DLNA/UPnP program, though (I forget what it's called: media player, or something like that).
The problem, however, is that the Roku's format list is really small, and likewise, I think what their DLNA "accepts" from MC (don't know the technical term for it) is pretty limited too, e.g., I just tried to play an MKVed blu-ray through my Roku, and while the film itself played fine, I got no subtitles (and there's no way to turn them on because it's not taking all that MC sends, since I have that option checked in MC's Options/Media Network).
Anyway, if you have music/video in their accepted formats and/or you don't mind transcoding on the fly, it should work.
