A normal data disc is fine for the PC but not for the xbox. You'd wanna make a xiso. Forget all that just get your hands on an autoinstaller disc. Slayers or Autoinstaller deluxe will do you just fine.
Use either of those disc's to install apps (xbmc,configmagic etc..). If its apps are too old then you can use
a program C-XBox Tool or Qwix to extract the disc onto your PC and replace the apps for more current ones.
Then you use the program to re-make the ISO and nero to burn it (or whatever fav burner prog you use).
Chuck it into the xbox and upgrade your apps only (if using slayers).
As you may have figure out by now you don't add an auto installer or there isnt a autoinstaller prog its an autoinstaller disc.
Now on the other hand if the xbox is modded in some way then you could simply DL the latest version of xbmc and ftp it over to the F: folder/apps and you'd be done. Just remember to name the xbmc file the same as the old one that you deleted. This may not be a problem if the dashboard auto searches for apps in the correct location.
Pheeew.... got all that?
Just keep asking if ya get stuck......And for god sake dont do anything if you not sure of what you doing!
Ask as many time as you need, but only execute it once