BMW bought the Rover Group back in the early-90s. The Rover Group included Rover, Land Rover, MINI, and MG. BMW poured billions into the group, but failed to turn a profit. In 1999, BMW sold the Rover Group with the exception of Land Rover to the Phoenix Consortium, a group of British venture capitalists. Since Land Rover was considered the "crown jewel" of the Group, BMW sold it for more money to the Ford Motor Company. Land Rover is now part of Ford's Premier Luxury Group, which also includes Jaguar, Aston Martin, and Volvo. The CEO of Ford's PLG is Wolfgang Reitzle, former VP at BMW. BMW had so much R&D in the New MINI when it sold the Rover Group, that it kept this portion. BMW also took Land Rover's Hill Decent Control.
At about the same time all this was going on, BMW tried to buy Rolls-Royce and Bently. Volks-Wagon offered more for the companies, but BMW was sneaky, and instead of allowing VW to take the whole cake, BMW bought the name "Rolls-Royce." BMW will begin offering cars under the brand in January 2003, and BMW owns a large portion of aircraft engine maker Rolls-Royce PLC.
N8Magic: MINI is actually its own brand. BMW wants to keep them separate if MINI is a failure, but to boost the perception of quality and performance, most people, like car magazines, tie the brands together.