A closer parallel of trinities in Hinduism and Buddhism woould be the rishi, devata, and chandas, of the Vedas, and the Trikaya of the Buddha Body of Dharmakaya, Sambogakaya, and Nirmanakaya. One cannot create any threefold god structure in Buddhism. That would be patently false and against the basic teachings of the Buddhadharma as always taught and explored. Those are the only two things I am able to comment upon.
There are two interesting websites I found recently which provide an 'interesting' point of view regarding the identity of the holy ghost. http://www.geocities.com/goddess_trixie2000/ChristianForest.html Specifically check this link out: http://www.geocities.com/goddess_trixie2000/FemaleHolySpirit.html I question this guy's beliefs. He is too 'fundamentalist' oriented for my tastes. Yet, I find some of his views thought-provoking: http://www.geocities.com/davidjayjordan/