You can use Horizon. It doesn't display the folder IDs but shows name of the folders instead and it has a Theme Creator. I prefer that over Xtaf.
Make sure your USB is configured in Xbox360.
Plug your USB in your PC or laptop.
Open Xtaf.
Click 'File' - > 'Open First USB Drive' or 'Open USB Manually' if you have problems opening it.
Once it opens the drive, expand Data Partition branch and you should see something like this.
Extend
0000000000000000 folder.
- next you should have an FFFE07DF folder. If you don't, create it like this:
and name it
FFFE07DF.
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NOTE:
If you previously downloaded Xbox 360 themes from Xbox Live they might be in a different folder. You can find that folder and save themes there instead of the
FFFE07 but it doesn't matter; Ithe Xbox will display the theme in the theme list anyway. That folder will have Content Title 'Themes' like this:
If you can't find that folder then save the themes in the
00030000 folder. You will notice that when you create
00030000 folder it's Content Title will be automatically set to 'Themes'.
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Go into
00030000 folder or create it inside
FFFE07DF.
- now minimize Xtaf and find your downloaded theme
- drag the selected theme and drop it in the right window.
And that's it. Now, when you plug the USB go to Social tab, and go to your Avatar. Under your Avatar option go to themes and your newly added themes should appear there.
You can also create themes with Modio. Google it, though, it is not that hard all you got to do is find the pictures you want and the rest is a piece of cake.