Open source developers are working to port Xbox Media Center (XBMC) to Mac OS X.
XBMC is software that's designed to run on a v.1 Xbox console. It's a free multimedia player for the console which can be used to play/view most common video, audio and image formats.
These include: MPEG-1/2/4, DivX, XviD, MP3, AAC, JPG, GIF plus many more less known formats directly from a CD/DVD in the Xbox' DVD-ROM drive or from its hard-drive.
XBMC can also stream files from a PC over a local network and stream media streams directly from the internet. The software offers playlist and slideshow functions, weather forecasts and music visualisation engines.
Developer "elan" has managed to tweak the Linux port of the software to run on an Intel Mac running Leopard, hoping to develop support for PowerPC Macs and Tiger in future.