Quick tutorial:
Use winrar. download it. install it.
your .rar files: each Wii game will be different.
Some more, some less, some poster's will have rar files of the whole 4.37GB of a game,
while others will have a "scrubbed" size of games = (smaller than 4.37GB).
so, example, Mario Kart my have 11 rar files, you need to DL ALL 11 files, all in the same folder.
now use winrar, or, simply right-click on the last file, choose "extract here", and winrar will build
the ISO. Some posters will double-compress files, but not many, simply extract here again, then the iso
should be there.
if you keep getting corrupted file prompts, the poster f'ed up, or some rar files need to be downloaded again, a .sfv file with the rar files is used to tell what files are corrupted. Not all posters include this file.
Once you have an .ISO, you can burn to dvd-r with imgburn, or use wii backup manager to transfer this iso to a hard drive (usb)