1) open the xbox (http://www.biline.ca/xbox_open.htm)
2) figure out which version xbox you have (http://www.biline.ca/xbox_version.htm)
3) 'solder' the correct pins on the motherboard (http://www.biline.ca/xbox_solder.htm)
4) put xbox back together.
5) copy the special savegame to the hard disk of the xbox (via usb key)
6) load splinter cell game then load the save game called 'linux'
7) once linux loads, you need to telnet into the xbox (its ip is 192.168.0.64)
8) you then need to type the following:

cd /media/E/UDATA/21585554/000000000000/raincoat/
raincoat -p somebios.bin

9) once it completes flashing (only takes a few seconds) you can reboot the xbox with the new bios.
10) backup all the data from your current hard disk
11) remove old hard disk, and put new one in its place
12) put "AutoInstaller Deluxe" or "Slayers AutoInstaller" disc in drive.
13) It will notice the new drive, and ask if you want to format it.
14) Once formatted, choose (outdated) software to install from its menu, or FTP latest XBMC to the xbox.