If you have a Plex server running on your network, with DLNA activated, and you have a Original Xbox running XBMC4Xbox, you can actually watch Plex from there.
Here's the profile I cooked up:
<?xml version="1.0" encoding="utf-8"?>
<!-- Save this as "OG Xbox.xml" and put it in the "C:\Users\username\AppData\Local\Plex Media Server\Profiles\" folder (create the Profiles folder if one does not exist -->
<!-- Tested with XBMC4Xbox 3.5.3 and Plex Media Server 1.4.3.3433 -->
<!-- Twitter: @djs__ -->
<Client name="OG Xbox">
<Identification>
<Header name="User-Agent" substring="(Xbox; http://www.xbmc.org)" />
</Identification>
<TranscodeTargets>
<VideoProfile container="mkv" codec="h264" audioCodec="ac3">
<Setting name="VideoEncodeFlags" value="-profile:v baseline -x264opts level=3.0:no-cabac=1" />
</VideoProfile>
<MusicProfile container="mp3" codec="mp3" />
<PhotoProfile container="jpeg" />
</TranscodeTargets>
<DirectPlayProfiles>
<VideoProfile container="*" codec="mpeg4" audioCodec="ac3,mp3" />
<MusicProfile container="*" codec="mp3,aac,wmav2,pcm,ogg" />
<PhotoProfile container="jpeg,png,gif,bmp,tiff" />
</DirectPlayProfiles>
<CodecProfiles>
<VideoCodec name="h264">
<Limitations>
<UpperBound name="video.width" value="720" isRequired="true" />
<UpperBound name="video.height" value="480" isRequired="true" />
<UpperBound name="video.level" value="30" isRequired="true" />
</Limitations>
</VideoCodec>
<VideoCodec name="mpeg4"> <!-- og xbox is actually quite capable of 1280x720 H263 -->
<Limitations>
<UpperBound name="video.width" value="1280" isRequired="true" />
<UpperBound name="video.height" value="720" isRequired="true" />
</Limitations>
<VideoAudioCodec name="mp3">
<Limitations>
<UpperBound name="audio.channels" value="2" isRequired="true" />
</Limitations>
</VideoAudioCodec>
<VideoAudioCodec name="ac3">
<Limitations>
<UpperBound name="audio.channels" value="6" />
</Limitations>
</VideoAudioCodec>
</VideoCodec>
</CodecProfiles>
</Client>
To use it, save it as "OG Xbox.xml" and put it in C:\Users\username\AppData\Local\Plex Media Server\Profiles\
(on Windows, figure it out on your own on other OSes) (create the Profiles folder if it does not exist.)
Let me run down quickly what it does:
Other than that, pretty much all music formats and image formats are natively supported
Known issues: - Seeking does not work (I've tried a bunch of settings and suggestions I found online but nothing worked) - All subtitles are burned in, even though XBMC can use SRT files and probably VOBSUB too. I tried passing through SRT files but XBMC didn't seem to pick them up (I'm guessing it has to do with XBMC4Xbox's DLNA implementation)
Enjoy... I guess.
I don't really recommend consuming media on the OG Xbox nowadays, as there are much better alternatives. But it's neat nonetheless to still atleast be able to use the OG Xbox for it.