What you need:
Windows Vista x64 or Windows 7 x64 operating system
a fast CPU (at least a dual core 2.6GHz processor)
an averrage GPU
Dolphin Emulator with Netplay support (Revision 6225)
GNT4 as an ISO (you can rip your original disc to your PC with a Wii homebrew application, google for more information)
internet connection
people who actually wants to play with you
First, download the emulator & the virtual memory card savestate of GNT4
(Note, this Emulator version is only for 64bit systems, there is a 32bit version available but then you must have an even faster CPU for full speed gameplay.)
Unzip Dolphin R6225.rar anywhere you want.
Now unzip MemoryCardA.JAP.rar into "Dolphin R6225\User\GC".
Start "Dolphin.exe".
A window appears.
Click on "Browse" and choose the directory your GNT4 game is located at, then click OK.
Your game now appears in the window.
If your monitor is cappable of 1920x1080 resolution and you are using the 360 Controller, skip this part:
Click on "Config" (the pliers icon), now go to the "Display" tab and choose your fullscreen resolution. Then click OK.
Now click on GCPad. Choose your gamepad by clicking on the arrow on "Device" next to the blank field.
Both players must use the same type of input, Xinput vs. Dinput does not sync.
Then set your buttons and analogsticks (you can even set rumble) and click on save.
End of part.
If you are using a router, the host must forward port 2626.
Now you're all set for netplay.
Click on "Tools" and then choose "Start NetPlay".
Here you can make your own Nickname.
If you want to host, click on "Host", choose the game (due to the japanese game, you will see some crazy random yiyiy or something, that's your GNT4 game).
Now the client must enter the host's IP adress. (if you don't know your IP,
http://www.ipchicken.com/ will tell you)
You will get a new chatwindow.
The host can change the button buffer on the buttom which influences the button delay, a low buffer means low delay.
I recommend buffer 7 on 30-60ms. (with this you can play as good as offline)
If the ping between you and your opponent is above 60ms (only the host can see the ping), setting pad buffer too low results a FPS drop and can cause desync.
When the host clicks on start, the game will automatically start for both players.
The host can end the game session for both players anytime by alt tabbing to the chatwindow and clicking on stop.
If you get a desync after a big lagspike or something, simply stop and start the game again.