Ford Motor Company, maker of such popular vehicles as the Mustang, Explorer, and F150 truck, announced this week that it will offer Sirius satellite radio as a factory-installed option in as many as 1 million vehicles over the next 2 years. The deal covers 21 vehicle models, which will start seeing Sirius installations beginning this summer. The deal is a huge win for Sirius, which is battling XM Radio in the suddenly lucrative satellite radio market. Sirius currently has more than 1 million subscribers, whereas XM boasts over 3 million