EVERYONE WHO HAS A HITACHI DRIVE PLEASE READ THIS!!!!
There is a way to play the game even with firmware revision 78/79, just follow these instructions and it works! I'm playing the game right now without any problems. Note: You need IXtreme 1.51 or it won't work (I assume most people have it already though).
This is taken from a member on xbox360iso
"As above for anyone with an hitachi that gives disk unreadable error after installing update from disk
All you need to do is download the padte from the xbox website
google 'xbox.com update'
or download from here
http://www.megaupload.com/?d=89HETOER
unzip to usb flash drive ,put it in your 360 & power on.
It would seem the one on the acb disk is not full,once youve installed the one from memory stick skip the tutorial & try your assassins creed disk again.
It does now work
I have both a 78 & 79 hitachi model both on ixtreme 1.51 & it works fine on both now."
Just do exactly as that states and you'll be able to play the game.