Tamang ni beauties with Damphurays
According to one school, Tamang is a corruption of the Tibetan work Ta-mangpo that is many horses. This theory holds that group of horsemen migrated from Tibet and settled down in Eastern Nepal and managed to take wives unto themselves. The off-springs were the Tamangs.
According to another school, the word Tamang is corrupt form of Tibetan word ‘Ta-Marpo’ meaning there by a herdsman looking after a herd of horse in the Himalayan pasture. This Ta- Marpo tribe crossed over the Himalayas and began to settle in Nepal. In the process of settlement, they married Nepali women. The children burnout of such marriages began to follow the religious practices of their fathers as well as the social customs of their mother (Hinduism).

Points to taken.
"The Tamang tribe of Nepal was brought to Kathmandu Valley by King Srong-sen Gampo of Tibet in the 7th century AD as a cavalry division. Their own tradition also says that their original habitat was in Southern Tibet in a place called Uichang. Tamang officers made Central Nepal their permanent settlement and settled around the Kathmandu valley and renamed villages after their names. Their villages were respectively called Moktan kipat, Bal kipat, Bomzan kipat, Ghising kipat, Pakhrin kipat, Yonzon kipat, Syangdan kipat, Thing kipat, Goley kipat, Giaba kipat, Mikchan kipat and Bozu kipat in the Chatara and Dhading districts. They ruled these villages till the Gurkha invasion in the west. Their kipat lands were annexed to the Gorkha Kingdom during the reign of King Prithvi Narayan Shah in 1768 AD". ~ The History of Kirat People, 2003

I also asked some Tamang elders about their ancestor and history. They told Ta - means Horse and Mang means, which looks after the horses. They are from Tibet and their ancestors got married with Hindu women and the new community was formed and that is Tamang. The Tamangs have their Mundum i.e. the song which describes their ancient past. They sing this song on religious and
social occasions to the rhythmic beats of their dear musical instrument Damphu (tambourine). Before singing of Tamang Selo (song) the name of Siva the god of all the Mongol Kirati tribes is invoked.

"O Siva the Almighty Lord !
We offer this song in your name,
This Damphu is not made of gold
Nor made
of silver,
It is made of the woods
of Koiralo and Jasing
and the skin of the mountain goat,
As U start playing a booming sound
filled the atmosphere,
This is the instrument of goddess Saraswati.
We do pray that
the sound of the Damphu
Will reach your ears"

Immediately
after the Damphurays (men playing the Damphoo) start singing the Mundum
(songs containing the ancient past) of the Tamangs starting from the
creation of this universe.

"Deep silence and darkness
Pervade all around.
The earth and the Dubo grass

Joined themselves
The sky and the mist
also mingled into each other
A tree then appeared
from the water.
As it was moving around
the grass and the water
caught hold of its roots
A lotus flower
Appeared from the water
on which sat the Almight Lord."

Work referenced:
"The History of the Kirat People", 2003