XBMC or X-Box Media Centre is a cross-platform media centre. Initially it was developed for old X-Box set. The new XBMC Atlantis release is the multi-platform compatible release. It's an open source endeavour and is highly customizable. It can be run on following platforms:
One of the three is a HD (High Definition) theme.
Another very useful feature is that, it can be set to download automatically the movie DVD cover art and other information from the net.
All the features including the background pictures of different media sections (video, music, movie , picture,weather and TV) can be changed and custom images can replace the default one.
It also has a section that displays local weather.
Unlike windows media centre , its highly responsive and fast. It takes only half of the RAM used by the Windows media centre ( I did check that! ).
But one feature I don't like is that the windowed and the full screen are two separate icons and there is no way you can go from one to the other.
If you would like to try, download from: Download XBMC.