Almost any image loader tutorial should cover the basics for something like BMP or TGA. Then you just need to replace the parsing of the TGA file with something suitable for the iff/ilbm image formats.
You can probably find a description of the image formats somewhere
WotSits formats (i category).
You could also try taking a look at the source for decoding those formats used in programs like the Gimp or Asset Importer.
Andy
EDIT: or rzookol could post that awesome that tells you just about everything you'll need :lol:
