I have a Quran in front me and you can easily find where something is mentioned in the Quran through websites like this: http://quran.com/

The Sabians are briefly mentioned in the Quran, 2:62, 5:69, 22:17 but a lot more information is given in Hadiths.

To answer your question the Sabians were considered the same as the Jews and Christians. They are all people of the book who believe in Allah, and their scriptures are revealed just like the Quran. Zoroastrianism and Manichaeism are not considered monotheistic religions (dualism) even though the Abrahamic religions are very closely related to Zoroastrianism. Zoroastrianism did however become tolerated and accepted in early Arab ruled Iran (they were not persecuted very much)

As for the Hadiths I cant remember which ones describe more about the Sabians.

Islam had a purpose of eradicating polytheism. Islam accepted all monotheistic faiths before Muhammad's time, which is why the Sabi religion is recognized.