Brewology

this is not my method but a very good..

Note that the best firmware for Homebrew is 3.2

First of all, you will need to install the Homebrew Channel (HBC)
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If you need help installing the homebrew channel, refer to Nito711's vid response Or use the twilight hack.
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DOWNGRADING WITH 3.3v3 OR 3.4
I added some new links.

After the HBC is installed on your Wii, delete everything on the card.

Step 1 - Download these files:
http://www.megaupload.com/?d=8OF7W3BP

Step 2 - Extract the wii downgrade.rar and drag the "apps" and "wad" folder on the SD card.

Step 3 - Using the Homebrew Channel, open WAD Manager 1.3

Step 4 - Press A on the Wii Mote once. The Wii should detect a SD Card. Press A again to see a list of WADs on the SD Card. Use the D-Pad to select IOS16-64-v257-prod.wad. Press the + to install the WAD. Once it has installed the WAD, press the Home button to restart you Wii.

Step 5 - Using the Homebrew Channel, open Custom WM. Now using the same method as in Step 4, install the cios_fix.wad. Once it has installed the WAD, press the Home button to restart you Wii.

Note: If that fails to install, just use 'Wad Manager 1.3'

Step 6 - Using the Homebrew Channel, open IOS Downgrader. Just follow the instructions and wait until it finishes installing the necessary IOSs.

NOTE: You're Wii does require connection to the Internet otherwise it won't work. Same for the next step.
If you do have a Internet connection and you get errors while it's installing the IOSs, just restart the Wii and try again.

Step 7 - Using the Homebrew Channel, open Install Shop IOS51. Say Yes to installing the IOS51 and Yes to patching a fix but No to the Wii Shop Channel (it shouldnt matter if you install but it wont make any difference).

Step 8 - Using the Homebrew Channel, open WAD Manager 3.

Step 9 - Now you should be able to install WADs. Try installing the WAD MANAGER V3.wad

Step 10 - Downgrade to 3.2 or whatever firmware you want. Make sure you choose the right region or you will semi-brick your Wii. (U = USA, E = Europe, J = Japan)
Use this file with the HBC to downgrade. Make sure you put it in a folder in the 'apps' folder.
You can also use AyRegion Changer to downgrade

That's the exact same tut I used to downgrade.

(how did you know?! ...lol)

Great tut ain't it???

I'm confuzzed.

i did all the way to step 9
and restarted the wii
however step 10 has completely escaped me !!!!!
do i need another wad or something?

It worked. But i think i did semi-brick my NinWii. Because i got a warning when the whole downgrading was finish. It said "Warning: Mistmatch in Area" or something. Hopefully there's a way i can fix this without sending my nintendo for repair. Anyway. Super tutorial. Thanks

And the nintendo wii is still alive. Just to say that xD

Their is a downgrader un Tutorials for 4.0. This one is for 3.3/3.4.