the original game is required to install the Homebrew Channel (HBC), once u have that installed, u don't need the original game with an exploit anymore. Also, a disc based exploit is only required if u are on 4.3, if u are on 3.0-4.2, u can use one of the versions of bannerbomb as an exploit instead of a disc.
A USB-Loader allows u to save Wii Games to a hard drive, then play them off of the hard drive without ever needing to use the original disc and risk scratching it.
A USB-Loader forwarder channel is installed a part of the ModMii Wizards extra brick protection, but unless you actually set up a usb-loader, the forwarder channel will not actually do anything. So after you mod your wii using the ModMii Wizard, use ModMii's USB-Loader Set up guide to help u set up a usb-loader. Once u do that, plug the hard drive into the bottom usb-port on your Wii, and start the usb-loader forwarder channel (or launch the usb-loader from the HBC) and it will start the USB-Loader. From there u can backup your original games to the hard drive and play them without needing the disc anymore.