You will find it in the usual places. It is labeled Gueux Hack-DevKiT Bios V2.
I wrote a program to compliment this called DevXSwitch. It will switch your debug kit in and out of debug mode. All you do is build the program and then drop it, the default.tbn, and the contents of the hackit package (xboxrom.bin and Gueux-E-drive-Volume-B.dxt) in a directory together. Then you can run DevXSwitch to enable the hackit bios and run it again to go back to xdk. Optionally you can drop a "dashboard.cfg" file into the folder that has a path to a dashboard. That dashboard will be the default boot app when you have the hackit mod enabled.
For example, if you installed XBMC into the default "Game Development" volume and you wanted it to be your dashboard when the hack-kit bios is enabled you would put this in the dashboard.cfg:
That would make it boot automatically to XBMC when the hackit bios is enabled and running DevXSwitch again will disable the mod and set it to boot to xdk again.
You can find the source for the application here: http://svn.huntsvegas.org/wsvn/DevXSwitch/trunk/
Backup anything important before you attempt to use these apps. If you need any help let me know. You can also PM me if necessary.