A new CVS compile (by T3CH) of xboxMediaCenter has been released.
This T3CH-compile is a BAREBONE package (so less stuff that can cause issues) compiled with XDK v5849.

Here's the added (including 'on-the-fly' unrarring support!) and updated stuff since the 2005-07-31 CVS release - for the full changelog including the fixed and changed stuff go to the forum thread:
* updated: libdvdcss for dvdplayer to v1.2.9
* updated: mplayer.dll to cvs version( new ffmpeg, interlaced flag, cache uninit fix)
* added: option to disable archive handling in media windows. useful for ccx+unrar.
* added: New video OSD settings/bookmarks menus.
* added: Control.HasFocus(controlID) and ButtonScroller.HasIcon(icon) conditional visibility items.
* added: httpapi: GetCurrentlyPlaying now provides both picture and audio information if music is being played during a slideshow
* added: subtitles can reside in "subs/","subtitles/","../subs/" and "../subtitles/".
* added: proper stored rar support.
* added: More stuff for the new video OSD system.
* added: Initial support for audio and subtitle settings to new video OSD layout (currently disabled)
* added: more memory error handling in DLLLoader, should avoid some hardlocks when mplayer crashes
* added: New conditional visibility tag Player.CodecInfo - true when in Visualisation and the codec info is up, or if you are in Slideshow and the file information is up.
* added: Fading for controls and dialogs in the GUI.
* added: file and socket tracking for dlls
... read the full changelog here

You can add more scripts and skins yourself if desired. You can download them from allxboxskins.com, xbox-skins.net and xbmcscripts.com.
Keep in mind this is a CVS snapshot of the current development tree. It's not a official (stable) point release. Use only if you know what you are doing.