More possible ways to port MediaPortal to Linux is discussed in this other topic thread:
MediaPortal under Linux?
However the answer from MediaPortal's developers remain;
anyone else is welcome to port MP to Linux but Team-MediaPortal will not do it themselves.
@spuck, off-topic but XBMC for Linux supports almost everything XBMC for Xbox does by now (and yes that includes handling downloaded TV-Series in library/database and file-mode really nice), but like Bram noted, there is no PVR support in XBMC, ...maybe someday it will be able to use MediaPortal and/or MythTV as a TV-server backend in a user-friendly way but that is nothing that we should discuss in this topic thread.
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Regards / Gamester17. Project Manager, The XBMC Project.
xbmc.org the official XBMC website and forums.