In a large saucepan, let the beans soak in enough cold water to cover for 1 hour and drain. Return the beans to the pan with the 8 cups of water and garlic. Bring the water to a boil, lower the heat, and simmer until tender, about 1 hour.
Meanwhile, heat the oil in a large heavy skillet over moderate heat. Add the pepper, onion, and cumin and cook, stirring, until softened.
Drain the beans and reserve 1/2 cup of them. Add the remaining beans to the pepper mixture with the remaining 1/4 cup water, and simmer, covered, until very tender, about 15 minutes.
In a food processor, blend bean mixture with the vinegar and pulse until well combined but not pureed smooth. Season the dip with salt, pepper, and vinegar. Transfer to a serving bowl, and stir in the reserved 1/2 cup beans. Let the dip cool to room temperature or chill.
When to serve, garnish the dip with the reserved bell pepper, onion, tomato, chile, cilantro leaves, and sour cream. Serve with the tortilla chips.
This dip may be made 2 days in advance and kept covered and chilled
Recipe courtesy of Gourmet Magazine