thanks to Yahoo Answers: It is not "El día de los muertos"!! It's: "Día de Brujas" (day of the witches).
From a 1998 article: Effect of Halloween on Mexico's Nov. 2 "Day of the Dead" explored by UC Berkeley anthropology professor
By Patricia McBroom, Public Affairs
BERKELEY -- Halloween costumes and plastic pumpkins have flooded into Mexico on the North American Free Trade Agreement's commercial tide, changing that country's Day of the Dead festivities. In response, Mexican nationals have united to stop what they view as "gringo imperialism," according to research by Professor Stanley Brandes, chairman of the Department of Anthropology at the University of California, Berkeley.
"All over Mexico today, there appears evidence of resistance to the Halloween invasion from the north," said Brandes, in an article published this month in the Journal of American Folklore. He said that clerics in several Mexican states have prohibited the celebration of Halloween on the grounds that it represents a threat to the sanctity of the Day of the Dead, traditionally held on November 2. In other signs of resistance, the city of Oaxaca moved to protect its competition for the best home altar - set up to honor the dead - by disqualifying any altar that presents "foreign elements."
By contrast, the huge department store chain, Sanborn, which caters to the Mexican urban, middle class, has begun large-scale marketing of Halloween costumes and candies throughout the country, said Brandes. In spite of Mexican resistance, he said, "Halloween has indeed become a palpable part of Day of the Dead festivities."
The two festivals share a common origin in the medieval Catholic holy days - All Saints' Day (Nov.1) and All Souls' Day (Nov. 2). Mexico's Day of the Dead refers to a combination of the two and normally is observed on Nov. 2. It includes special masses to honor souls in purgatory, complemented by folk rituals, such as decorating graves, setting up home altars and sculpting sugar candies in the form of skulls, skeletons and caskets.
Halloween, which occurs on the eve of All Saints' Day (Oct. 31), draws its origins from the pre-Christian holiday called Samhain, celebrated by the Celts of Ireland, Scotland and Wales.