This is the method I used to install USB Loader GX and load my game disks onto a USB hard drive.
Update the Wii to 4.3E or your equivalent. Go into the network settings and write down the MAC address of the console.
Format a 2GB SDCARD and a much larger USB drive as FAT32. Use gparted in Linux, Windows won't work for big drives.
Visit HackMii and download the HackMii bundle using the data gathered above.
Copy the files onto the 2GB SDCARD and load into the console.
Visit the messages section and open the message with the red bomb icon.
Install the Homebrew channel and BootMii applications from the menu. On early Wiis we can install BootMii in the bootloader and as an IOS, for later Wiis, only as an IOS.
Restart the Wii, enter the Homebrew channel and run BootMii from the menu.
When BootMii runs, the controller doesn't operate, use the power button to move and the reset button to select the NAND backup sub-menu.
Backup the NAND to the SDCARD, this will take a while and don't worry about bad blocks, it's normal.
I haven't used this backup but it seems sensible to create this.
From the Homebrew channel install priiloader. This will be used via the RESET button to jump into the the Homebrew channel in case of any emergencies. This is important when we cannot patch the bootloader.
Fetch `d2x cIOS Installer v3.1.zip' and unzip on SDCARD, likewise fetch `USBLoader_GX_V3_0_AllinOnePackage_IOS249.zip' and do the same. Using 7zip, also update d2x with d2x-v10-beta52.zip
These will be Homebrew applications.
Start up Wii and enter Homebrew, run d2x and install it into IOS slot 249 base 56. Also install IOS slot 250 base 57 if required.
After a restart you can test USB Loader and begin ripping game disks to the USB hard drive. If USB Loader can't find your USB drive, swap the USB port.
Download yet another Wii module manager `YAWMM.zip' and unzip on SDCARD.
Run this from Homebrew, navigate to the wad directory and load the forwarder for IOS 249.
The Wii will now be able to run the Loader direct from the main menu.