The following is an actual question, not a cheap rationale for piracy. I geniunely don't know the answer to this.
It is my understanding that certain materials in every d20 book are public domain, that is, the author makes no claim to copyright ownership. Typically, these are the "crunchy bits" spells, feats, classes, etc. This is delineated at the beginning of the manuscript.
If you download the PDF (say from Kazaa) and then keep only the "open" material (and even perhaps distribute this material to your group along with the Liscence) have you violated any laws? Would it be legal to download PDFs, create your own campaing book of crunchy bits, and then send this (along with the liscence) to whomever you chose?