RTFM.
www.xboxmediacenter.de FFS, do some searching before you ask... but anyways i'll answer your question.
If you want to install XBMC as your dash....
1. Download and extract it to your desktop somewhere.
2. Edit the xboxmediacenter.xml to suit your needs. One important setting to fix up is the <home> </home>. This tells the main xbe where to find the rest of the dash files. I use <home>E:\Apps\XBMC\</home>
3. Rename the default.xbe to xbmc.xbe
4. Upload xbmc.xbe and xboxmediacenter.xml to C:\
5. Upload all the other files and folders in the distro to E:\Apps\XBMC\
6. Put xbmc.xbe at the top of your x3cl boot order.
If you want to just install it as an application...
1. Download and extract it to your desktop somewhere.
2. FTP all the files to E:\Apps\XBMC\
3. Go to your dash and launch the default.xbe in the xbmc folder.
