Reb Doniel,
There are different types of Buddhism. Zen Buddhism (i.e. the American form) is “non-theistic” but Tibetian Buddhism is theistic and is avoda zarah. Read “The Jew and the Lotus” the description of a Jewish Delegation that goes to meet the Dalai Lama.
Hinduism is at the early stage of Avoda Zara described by the Rambam in the beginning of sefer Mada. They believe that there is one real G-d who created everything but who is too awesome for mere mortals to relate to. Therefore there are many little gods that interact with people on a day to day level.