I think the Campbell book's dreadful. Turgid, tedious, badly laid out, not enough and not clear enough diagrams, hugely verbose, heavily influenced by 1950s RAF attitudes, too big and not bound well enough.
If you want free stuff try:
http://www.caa.govt.nz/pilots/Instru...1_compiled.pdf
and
http://www.casa.gov.au/aoc/training/guides/fim.htm
Both good, but the NZ one's better cos it has diagrams.
NS