ok first get the xebian iso from here
then burn it onto a cd.
Do not extract the cd files from the cd to your hard drive. Boot it from the live cd and wait for the desktop.
Then click on the terminal. Type exactly what is written here (except for the directions) but dont include quotation marks:
if you have a later version of xebian (version 1.1.4 and up) the type: "xebian" for the password
then, type "XBOXLinuxInstall" these are case sensitive letters-include the capitals.
then you will be shown a couple of directions on how to install. Choose the first option if you still want xbmc to boot up. Then go through the rest of the instructions. When the installation starts, it will take from 5 minutes to 30 depending on the type you chose.
When it is over, it will ask you for the ip address just leave it as it is, you won't get Firefox to work unless you have a dhcp address (trust me, I've tried it).
To change the static to a dhcp address and not cause any conflicts with your other computers, then click here
There is a full explanation of what I just explained here
I hope that helped...