FYI: the Item Tool editing tools have been discontinued.
For a number of reasons, they are too complicated to use, discuss and share the results.
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OLD CONTENT:
ITEM_Tool and LMT early alpha version - ALPHA 2
http://www.aibohack.com/wii/itemtool.htm
Bug fixes in tools, a few more tutorials written.
For Hat editing, check out out tutorial #8 with a workaround http://www.aibohack.com/wii/itemtool.htm#TUT8
The main tutorials are written for USB Gecko owners only.
Supports US/NA version and EU/UK/OZ PAL version. Japanese version maybe later (ie. RUUE or RUUP only. Not RUUJ)
For people without a USB Gecko, you can use the slow process of uploading to a gamesave. This will give you a flavor of what is possible. The results are the same as the USB Gecko approach, but the process is much much slower.
http://www.aibohack.com/wii/itemtool_slow.htm