firstly you will need to softmod your wii using the guides on this site. this one should do it for you:
Once you have done this mod, i'm assuming it's a new wii here and you have not updated it, you will need to install a program (or channel) capable of loading from USB. My favourite for this is USB Loader GX. you will then need to format an external Hard Drive using one of the many Hard Drive tools available such as WBFS Manager.
If it is a new wii your new DVD-Rs will be useless as the new wiis are unable to read them thanks to Nintendo shipping them with newer drives.