You can incorporate any set beliefs or ways of worship into your life without becoming a recognized member of the religion. For example, if you want to work with a "Great Spirit" or Buffalo Woman - find equivalents that speak to your mind = Higher Power, Great Creator, God, Most Highest, Zeus; Epona, Diana, Freya, Great Mother, etc. You'd find it difficult to find books that outline most Indian religions, they are very closed about most of the inner workings of their beliefs.
You might check out books on shamanism. There is a rich history and active shaman beliefs and worship in Northern Europe and northern Russia with the Finns and Laplanders and there is a shaman working system in Asatru called Seidr (pronounced Say-th). South American shamanism is written about by Carlos Castanos (sp?), I believe.
When working in paganism, you can adapt as to what works for you within the basics of worship/ritual workings. In recon pagan religions and Indian religions you get a more narrow range of working that's accepted by those in the religion.
card carrying tribal member