Well I just finished my first Jtag attempt. It was successful so now I am here to help the community that helped me.
Here is short, simple tutorial on how to use your DLC content on your Jtag console
Credits
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All of the devs/researchers that aided in the Jtag foundation.
Me for writing this tutorial
Zouzzz for the program we will be using.
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Tutorial
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Alright first off we need to find where your purchased DLC content is located
In this picture I have located the Halo 3 map packs that I have purchased.
What to do first is to extract the content you wish to use on your jtag to a folder called "DLC"
Then go to this
link and extract the download once it is finished.
Once extracted run the program.
Navigate the program to your DLC folder and hit the red shaded button with the word "hex" in it.
Once it says "Done" you have done it just inject it to where you found it but rename it.
NOTE I will not offer support to those who stole DLC data.
Also if this doesn't work backup you data/dlc and stuff formatt your Xbox HDD on a retail console using that (retail) consoles serial and such. Recover an account on that HDD to get the folder integrity setup and then place in your DLC.