"dia de muertos" is a old tradition, it says basically the deads come to your house, you give them bread, wine, books, cds, or whatever they liked when they were alive. Also candles and a photograph of the person in question should be placed in the altar.
There should be a road made of tzempatzuchitls flowers, so they know the way from the cementery to your house and back to the cementery again.
There are too many details in this "dia de muertos" thing, i don't know them all, but it seems to be an international attraction, because Tzintzuntzan is full of tourists in those days.