If you are looking for authoritative information on the Magical Net, Gyurme Dorje's introduction to the Guhyagarbha Tantra is online, courtesy of the Wisdom Books library. Follow this link.
There are a number of useful references on this site, including a mature discussion of tulkus using Trungpa Rinpoche's typology of named tulkus, blessed tulkus, and direct tulkus.
