Here's a page on interesting Tibetan myths:
http://www.iras.ucalgary.ca/~volk/sylvia/Tib.htm
and two images of Lha:
http://images.google.com/imgres?imgu...%3D2%26hl%3Den
http://www.tharlam.org/Documents/whiteTara.jpg
Here's a page of Tibetan icons of various guardian "demons":
http://images.google.com/imgres?imgu...%3D2%26hl%3Den
Lhas are just the name for gods/spirits. There are various types:
According to Encyclopedia Mythica:
Thab-Lha is a Tibetan Bon hearth-god that punishes those who desecrate his sacred fires. He's pictured as a red figure with a snake in his hand.
Nang-Lha is a house god who's portrayed as a man with the head of a pig. People offer him beverages.
I couldn't find anything on dre, other than it's a countryside demon that drives away horses, or anything specific about 'gnod-sbyin', but the Bon Tibetan religion has quite a few interesting demons, from the Citipati (graveyard demons depicted as dancing skeletons) to the 'gNyan'-dMu class (country-god) spirits who bring disease and death to humanity.
Here's an image of Bon demons:
http://en.tibet.cn/newfeature/xzt_co...9962564293.jpg
and the Encyclopedia Mythica page on the dMu:
http://www.pantheon.org/articles/m/mu.html
I hope that helps!